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Book \ n 3 . 







AUTHOR OF "cooperage'" 



25 Park Place 






/^. J/02^ 


The seasoning and kiln-drying of wood is such an im- 
portant process in the manufacture of woods that a need 
for fuller information regarding it, based upon scientific 
study of the behavior of various species at different me- 
chanical temperatures, and under different drying proc- 
esses, is keenly felt. Everyone connected with the wood- 
working industry, or its use in manufactured products, 
is well aware of the difficulties encountered in properly 
seasoning or removing the moisture content without injury 
to the timber, and of its susceptibility to atmospheric con- 
ditions after it has been thoroughly seasoned. There is 
perhaps no material or substance that gives up its moisture 
with more resistance than wood does. It vigorously defies 
the efforts of human ingenuity to take away from it, without 
injury or destruction, that with which nature has so 
generously supplied it. 

In the past but little has been known of this matter 
further than the fact that wood contained moisture which 
had to be removed before the wood could be made use of 
for commercial purposes. Within recent years, however, 
considerable interest has been awakened among wood- 
users in the operation of kiln-drying. The losses occa.- 
sioned in air-drying and improper kiln-drying, and the 
necessity for getting the material dry as quickly as pofev 
sible after it has come from the saw, in order to prepare 
it for manufacturing purposes, are bringing about a realiza- 
tion of the importance of a technical knowledge of the 

The author desires to express his acknowledgement to the 
various Government reports indicated below, from all of 
which he has made liberal extracts : 


"The Kiln-drying of Gum," by James E. Imre, The United States 
Dept. of Agricultm-e, Division of Forestry. 

"The Structure of the Common Woods," by Reuben P. Prichard. 
The United States Dept. of Agriculture, Division of For- 
estry, Bulletin No. 3. 

"Timber," by Filbert Roth, The United States Dept. of Agri- 
culture, Division of Forestry, Bulletin No. 10. 

"The Effects of Moisture upon the Strength and Stiffness of 
Wood," by H. D. Tieman, The United States Dept. of 
Agriculture, Division of Forestry, Bulletin No. 70. 

"Principles of Kiln-drying Lumber," by H. D. Tieman, The 
United States Dept. of Agriculture, Division of Forestry. 

"The Theory of Drying and its Application, etc.," by H. D. 
Tieman, The United States Dept. of Agriculture, Division 
of Forestry, Bulletin No. 509. 

"Check List of the Forest Trees of the United States," The United 
States Dept. of Agriculture, Division of Forestry. 

Bulletin No. 37, The United States Dept. of Agriculture, Division 
of Forestry. 

"Seasoning of Timbers," by Herman Von Schrenk, The United 
States Dept. of Agriculture, Division of Forestry, Bulletin 
No. 41. 

Throughout the book the aim has been to give facts, and 
wherever a machine or appliance has been illustrated or 
commented upon, or the name of the makers mentioned, 
it has not been with the intention either of recommending 
or disparaging his or their work, but was used merely as an 
aid in illustrating the text. 

Readers who desire a more extended treatise on the 
subject will find Dr. Tiemann's ''Kiln Drying of Lumber" 
an invaluable aid. 



Section I 


Characteristics and Properties of Same — ^ Structure of Wood — Prop- 
erties of Wood — Classes of Trees 1-7 

Section II 


Wood of Coniferous Trees — Bark and Pith — Sapwood and Heart- 
wood — The Annual or Yearly Ring — Spring- and Summer- Wood 

— Anatomical Structure — List of Important Coniferous Trees . 8-30 

Section III 


Wood of Broad-leaved Trees — Minute Structure — List of Most Im- 
portant Broad-leaved Trees — Red Gum — ■ Range of Red Gum 

— Form of Red Gum — Tolerance of Red Gum — Its Demands 
upon Soil and Moisture — Reproduction of Red Gum — Second- 
growth Red Gum — Tupelo Gimi — Uses of Tupelo Gum — Range 

of Tupelo Gum 31-85 

Section IV 

Different Grains of Wood — Color and Odor of Wood — Weight of Wood 

— Weight of Kiln-dried Wood of Different Species — Figure in 
Wood 86-97 

Section V 


General Remarks — Ambrosia or Timber Beetles — Round-headed 
Borers — Flat-headed Borers — Timber Worms — Powder Post 
Borers — Conditions Favorable for Insect Injury — Crude Products 

— Round Timber with Bark on — How to Prevent Injiiry — 
Saplings — Stave, Heading, and Shingle Bolts — Unseasoned 
Products in the Rough — Seasoned Products in the Rough — Dry 
Cooperage Stock and Wooden Truss Hoops — Staves and Heads 

of Barrels Containing Alcohohc Liquids 98-113 


Section VI 


Distribution of Water in Wood — Seasonal Distribution of Water in 
Wood — Composition of Sap — Effects of Moisture on Wood — 
The Fibre-Saturation Point in Wood 114-118 

Section VII 


What Seasoning Is — Difference Between Seasoned and Unseasoned 
Wood — Manner of Evaporation of Water — Absorption of Water 
by Dry Wood — ■ Rapidity of Evaporation — Physical Properties 
that Influence Drjdng 119-127 

Section VIII 


Advantages of Seasoning — Prevention of Checking and Splitting — 
Shrinkage of Wood — Expansion of Wood — Elimination of 
Stain and Mildew 128-137 

Section IX 


Difficulties of Drying Wood — Changes Rendering Drying Difficult — 
Losses Due to Improper Kiln-drying — Properties of Wood that 
Effect Drying — Unsolved Problems in Kiln-drying 138-144 

Section X 

Methods of Drjdng — Drying at Atmospheric Pressure — Drying Under 
Pressure and Vacuum. — Impregnation Methods — Preliminary 
Treatments — Out-of-door Seasoning 145-155 

Section XI 


Advantages of Kiln-drjdng over Air Drying — Physical Conditions 
Governing the Drying of Wood — Theory of Kiln-drying — Re- 
quirements in a Satisfactory Dry Kiln — Kiln-drying — ■ Remarks 
— Underlying Principles — Objects of Kiln-drying — Conditions 
of Success — Different Treatments According to Kind — Tempera- 
ture Depends — Air Circulation — Humidity — • Kiln-drying — 
Pounds of Water Lost in Drying 100 Pounds of Green Wood in the 
Kaln — Kiln-drying Gum — Preliminary Steaming — ■ Final Steam- 
ing — Kiln-drymg of Green Red Gum 156-184 


Section XII 

Different types of Dry Kilns — The "Blower" or "Hot Blast" Dry 
Kiln — Operating the "Blower" or "Hot Blast" Dry KUn — The 
"Pipe" or "Moist-Air" Dry Kiln — Operating the "Pipe" or 
"Moist-Air" Dry Kiln — Choice of Drying Method — Kilns of 
Different Types — The "Progressive" Dry Kiln — The "Apart- 
ment" Dry Kiln — The "Pocket" Dry Kiln — The "Tower" 
Dry Kiln — The "Box" Dry Kiln 185-205 

Section XIII 


Kiln Cars and Method of Loading Same — The "Cross- wise" Piling 
Method — The "End-wise" Piling Method — The "Edge-wise" 
PiUng Method — ■ The Automatic Lumber Stacker — The Un- 
stacker Car — Stave Piling — Shingle Piling — Stave Bolt Trucks 
— Different Types of Kiln Cars — Different Types of Transfer 
Cars — Dry Kiln Doors — Different Types of KUn Door Carriers 206-236 

Section XIV 


The Himiidity Diagram — Examples of Use — The Hygrodeik — The 
Recording Hygrometer — - The Registering Hygrometer — The 
Recording Thermometer — The Registering Thermometer — 
The Recording Steam Gauge — The Troemroid Scalometer — Test 
Samples — Weighing — Examples of Use — Records of Moisture 
Content — Saw Mills — Factories — The Electric Heater . . , 237-250 

Section XV 

Bibliography — Glossary — Index of Latin Names — Index of Common 

Names 251-257 



1. Board of pine 13 

2. Wood of spruce 14 

3. Group of fibres from pine wood 15 

4. Block of oak 31 

5. Board of oak 32 

6. Cross-section of oak highly magnified 32 

7. Highly magnified fibres of wood 33 

8. Isolated fibres and cells of wood 34 

9. Cross-section of basswood 35 

10. A large red gum . 52 

11. A tupelo gum slough 53 

12. Second growth red gum 57 

13. A C3npress slough in dry season 58 

14. A large cottonwood 78 

15. Spiral grain in wood 87 

16. Alternating spiral grain in cypress 87 

17. Wavy grain in beech 88 

18. Section of wood showing position of the grain at base of limb . .- 89 

19. Cross-section of a group of wood fibres 91 

20. Isolated fibres of wood 91 

21. Orientation of wood samples 93 

22. Work of ambrosia beetles in tulip or yellow poplar 100 

23. Work of ambrosia beetles in oak 100 

24. Work of round-headed and flat-headed borers in pine 102 

25. Work of timber worms in oak 103 

26. Work of powder post borers in hickory poles 104 

27. Work of powder post borers in hickory poles . 104 

28. Work of powder post borers in hickory handles. ........ 105 

29. Work of round-headed borers in white pine staves ....... Ill 

30. U. S. Forest Service humidity controlled dry kiln . 161 

31. Section through moist-air dry kiln 189 

32. Live steam single pipe heating apparatus 190 

33. Live steam double pipe heating apparatus 191 

34. Vertical pipe heating apparatus 193 

35. Progressive dry kilns 197 

36. Apartment dry kilns 199 

37. Pocket dry kilns 201 

38. Tower dry kiln = . 203 

39. BoxdrykUn 205 

40. Edge-wise method of piling 206 


41. Edge-wise method of piling 207 

42. Automatic kmil)er stacker 208 

43. Automatic lumber stacker 208 

44. Battery of three automatic lumber stackers 209 

45. Battery of three automatic lumber stackers 209 

46. Lumber loaded edge-wise on kiln truck 210 

47. The lumber unstacker 211 

48. The lumber unstacker car 211 

49. Method of pihng veneer on edge 212 

50. Kiln truck loaded cross-wise of kiln 213 

51. Kiln truck loaded cross-wise of kiln 214 

52. Iviln truck loaded end-wise of kiln 214 

53. Kiln truck loaded end-wise of kiln 215 

54. Method of piling staves on kiln truck 216 

55. Method of piling staves on kiln truck 216 

56. Method of pihng tub or pail staves on kiln truck 217 

57. Method of piling bundled staves on kiln truck 217 

58. Method of pihng shingles on kiln truck 218 

59. Method of pihng shingles on kiln truck 218 

60. Method of piling shingles on kiln truck 219 

61. Kiln truck designed for loose pail staves 219 

62. K iln truck designed for handhng short stock 221 

63. Stave bolt truck 221 

64. Stave bolt truck 222 

65. Stave bolt truck 222 

66. Stave bolt truck ■ 223 

67. Stave bolt truck 223 

68. Stave bolt truck 224 

69. Regular 3-rail transfer car 224 

70. Regular 3-rail transfer car 225 

71. Special 4-rail transfer car 225 

72. Regular 2-rail transfer car 225 

73. Regular 2-rail transfer car 226 

74. Underslung type 3-rail transfer car 226 

75. Underslung type 2-rail transfer car 226 

76. Flexible type 2-rail transfer car 227 

77. Regular transfer car for stave bolt trucks 228 

78. Regular transfer car for stave bolt trucks 228 

79. Special transfer car for stave bolt trucks 228 

80. Regular channel iron kiln truck for cross-wise piling 229 

81. Regular channel iron kiln truck for cross-wise piling 229 

82. Regular channel iron kiln truck for end-wise piling 230 

83. Special channel iron kiln truck for end-wise piling 230 

84. Regular dolly kiln truck for end-wise pihng 230 

85. Asbestos-lined kiln door 231 

86. Twin door carrier with door loaded 232 

87. Twin door carrier for doors 18 to 35 feet wide 232 

88. Kiln door carrier 233 

89. Kiln door construction 234 

90. Kiln door construction 235 

91. Kiln door construction 235 

92. Iviln door construction 236 


93. The Humidity diagram . facing 237 

94. The hygrodeik 242 

95. The recording hygrometer 243 

96. The registering hygrometer 244 

97. The recording thermometer 245 

98. The registering thermometer 246 

99. The recording steam gauge 246 

100. The troemroid scalometer 247 

101. The electric heater 250 




Characteristics and Properties 

Timber was probably one of the earhest, if not the 
earhest, of materials used by man for constructional pur- 
poses. With it he built for himself a shelter from the 
elements; it provided him with fuel and ofttimes food, 
and the tree cut down and let across a stream formed the 
first bridge. From it, too, he made his "dug-out" to 
travel along and across the rivers of the district in which 
he dwelt; so on down through the ages, for shipbuilding 
and constructive purposes, timber has continued to our 
own time to be one of the most largely used of nature's 

Although wood has been in use so long and so universally, 
there still exists a remarkable lack of knowledge regard- 
ing its nature, not only among ordinary workmen, but 
among those who might be expected to know its proper- 
ties. Consequently it is often used in a faulty and waste- 
ful manner. Experience has been almost the only teacher, 
and theories — sometimes right, sometimes wrong — 
rather than well substantiated facts, lead the workman. 

One reason for this imperfect knowledge hes in the fact 
that wood is not a homogeneous material, but a compli- 
cated structure, and so variable that one piece will behave 
very differently from another, although cut from the same 
tree. Not only does the wood of one species differ from 
that of another, but the butt cut differs from that of the 
top log, the heartwood from the sapwood; the wood of 
the quickly-grown sapUng of the abandoned field, from 


that of the slowly-grown, old monarch of the forest. Even 
the manner in which the tree was cut and kept influences 
its behavior and quality. It is therefore extremely dif- 
ficult to study the material for the purpose of estabhsh- 
ing general laws. 

The experienced woodsman will look for straight- 
grained, long-fibred woods, with the absence of disturb- 
ing resinous and coloring matter, knots, etc., and will 
quickly distinguish the more porous red or black oaks from 
the less porous white species, Quercus alba. That the 
inspection should have regard to defects and unhealthy 
conditions (often indicated by color) goes without saying, 
and such inspection is usually practised. That knots, 
even the smallest, are defects, which for some uses con- 
demn the material entirely, need hardly be mentioned. 
But that '' season-checks," even those that have closed 
by subsequent shrinkage, remain elements of weakness 
is not so readily appreciated; yet there cannot be any 
doubt of this, since these, the intimate connections of 
the wood fibres, when once interrupted are never re- 

Careful woods-foremen and manufacturers, therefore, 
are concerned as to the manner in which their timber is 
treated after the felling, for, according to the more or less 
careful seasoning of it, the season checks — not altogether 
avoidable — are more or less abundant. 

There is no country where wood is more lavishly used 
or criminally neglected than in the United States, and 
none in which nature has more bountifully provided for 
all reasonable requirements. 

In the absence of proper efforts to secure reproduction, 
the most valuable kinds are rapidly being decimated, and 
the necessity of a more rational and careful use of what 
remains is clearly apparent. By greater care in selection, 
however, not only will the duration of the supply be ex- 
tended, but more satisfactory results will accrue from its 

There are few more extensive and wide-reaching sub- 
jects on which to treat than timber, which in this book 
refers to dead timber — • the timber of commerce — as 


distinct from the living tree. Such a great number of 
different kinds of wood are now being brought from various 
parts of the world, so many new kinds are continually 
being added, and the subject is more difficult to explain 
because timber of practically the same character which 
comes from different localities goes under different names, 
that if one were always to adhere to the botanical name 
there would be less confusion, although even botanists 
differ in some cases as to names. Except in the cases of 
the older and better known timbers, one rarely takes up 
two books dealing with timber and finds the botanical 
names the same; moreover, trees of the same species may 
produce a much poorer quality of timber when obtained 
from different localities in the same country, so that botani- 
cal knowledge will not always allow us to dispense with 
other tests. 

The structure of wood affords the only reliable means 
of distinguishing the different kinds. Color, weight, smell, 
and other appearances, which are often direct or indirect 
results of structure, may be helpful in this distinction, 
but cannot be relied upon entirely. Furthermore, struc- 
ture underlies nearly all the technical properties of this 
important product, and furnishes an explanation why one 
piece differs in these properties from another. Structure 
explains why oak is heavier, stronger, and tougher than 
pine; why it is harder to saw and plane, and why it is so 
much more difficult to season without injury. From its 
less porous structure alone it is evident that a piece of 
young and thrifty oak is stronger than the porous wood 
of an old or stunted tree, or that a Georgia or long-leaf 
pine excels white pine in weight and strength. 

Keeping especially in mind the arrangement and direc- 
tion of the fibres of wood, it is clear at once why knots and 
"cross-grain" interfere with the strength of timber. It 
is due to the structural peculiarities that ''honey-combing" 
occurs in rapid seasoning, that checks or cracks extend 
radially and follow pith rays, that tangent or "bastard" 
cut stock shrinks and warps more than that which is 
quarter-sawn. These same peculiarities enable oak to 
take a better finish than basswood or coarse-grained pine. 


Structure of Wood 

The softwoods are made up chiefly of tracheids, or 
vertical cells closed at the ends, and of the relatively short 
parenchyma cells of the medullary rays which extend 
radially from the heart of the tree. The course of the 
tracheids and the rays are at right angles to each other. 
Although the tracheids have their permeable portions or 
pits in their walls, liquids cannot pass through them with 
the greatest ease. The softwoods do not contain ''pores" 
or vessels and are therefore called "non-porous" woods. 

The hardwoods are not so simple in structure as soft- 
woods. They contain not only rays, and in many cases 
tracheids, but also thick-walled cells called fibres and wood 
parenchyma for the storage of such foods as starches and 
sugars. The principal structural features of the hard- 
woods are the pores or vessels. These are long tubes, the 
segments of which are made up of cells which have lost 
their end walls and joined end to end, forming continuous 
"pipe lines" from the roots to the leaves in the tree. Since 
they possess pores or vessels, the hardwoods are called 
"porous" woods. 

Red oak is an excellent example of a porous wood. In 
white oak the vessels of the heartwood especially are 
closed, very generally by ingrowths called tyloses. This 
probably explains why red oak dries more easily and 
rapidly than white oak. 

The red and black gums are perhaps the simplest of the 
hardwoods in structure. They are termed "diffuse po- 
rous" woods because of the numerous scattered pores 
they contain. They have only vessels, wood fibres, and 
a few parenchyma cells. The medullary rays, although 
present, are scarcely visible in most instances. The 
vessels are in many cases open, and might be expected to 
offer relatively little resistance to drying. 

Properties of Wood 

Certain general properties of wood may be discussed 
briefly. We know that wood substance has the property 
of taking in moisture from the air until some balance is 

TIMBER .- 5 

reached between the humidity of the air and the moisture 
in the wood. This moisture which goes into the cell walls 
is hygroscopic moisture, and the property which the wood 
substance has of taking on hygroscopic moisture is termed 
hygroscopicity. Usually wood contains not only hy- 
groscopic moisture but also more or less free water in the 
cell cavities. Especially is this true of sapwood. The 
free water usually dries out quite rapidly with little or no 
shrinkage or other physical change. 

In certain woods — for example, Eucalyptus globulus and 
possibly some oaks — shrinkage begins almost at once, thus 
introducing a factor at the very start of the seasoning proc- 
ess which makes these woods very refractory. 

The cell walls of some species, including the two already 
mentioned, such as Western red cedar and redwood, be- 
come soft and plastic when hot and moist. If the fibres 
are hot enough and very wet, they are not strong enough 
to withstand the resulting force of the atmospheric pres- 
sure and the tensile force exerted by the departing free 
water, and the result is that the cells actually collapse. 

In general, however, the hygroscopic moisture neces- 
sary to saturate the cell walls is termed the "fibre satura- 
tion point." This amount has been found to be from 
25 to 30 per cent of the dry wood weight. Unlike Eu- 
calyptus globulus and certain oaks, the gums do not begin 
to shrink until the moisture content has been reduced to 
about 30 per cent of the dry wood weight. These woods 
are not subject to collapse, although their fibres become 
very plastic while hot and moist. 

Upon the peculiar properties of each wood depends the 
difficulty or ease of the seasoning process. 

Classes of Trees 

The timber of the United States is furnished by three 
well-defined classes of trees : (1) The needle-leaved, naked- 
seeded conifers, such as pine, cedar, etc., (2) the broad- 
leaved trees, such as oak, poplar, etc., and (3) to an 
inferior extent by the (one-seed leaf) palms, yuccas, 
and their allies, which are confined to the most southern 
parts of the country. 


Broad-leaved trees are also known as deciduous trees, 
although, especially in warm countries, many of them are 
evergreen, while the needle-leaved trees (conifers) are 
commonly termed "evergreens," although the larch, bald 
cypress, and others shed their leaves every fall, and even 
the names "broad-leaved" and "coniferous," though per- 
haps the most satisfactory, are not at all exact, for the 
conifer "ginkgo" has broad leaves and bears no cones. 

Among the woodsmen, the woods of broad-leaved trees 
are known as ''hardwoods," though poplar is as soft as 
pine, and the "coniferous woods" are known as "soft- 
woods," notwithstanding the fact that yew ranks high in 
hardness even when compared with "hardwoods." 

Both in the number of different kinds of trees or species 
and still more in the importance of their product, the coni- 
fers and broad-leaved trees far excel the palms and their 

In the manner of their growth both the conifers and 
broad-leaved trees behave alike, adding each year a new 
layer of wood, which covers the old wood in all parts of 
the stem and limbs. Thus the trunk continues to grow 
in thickness throughout the life of the tree by additions 
(annual rings), which in temperate chmates are, barring 
accidents, accurate records of the tree. With the palms 
and their relatives the stem remains generally of the same 
diameter, the tree of a hundred years old being as thick 
as it was at ten years, the growth of these being only at 
the top. Even where a peripheral increase takes place, 
as in the yuccas, the wood is not laid on in well-defined 
layers for the structure remains irregular throughout. 
Though alike in the manner of their growth, and therefore 
similar in their general make-up, conifers and broad-leaved 
trees differ markedly in the details of their structure and 
the character of their wood. 

The wood of all conifers is very simple in its structure, 
the fibres composing the main part of the wood all being 
alike and their arrangement regular. The wood of the 
broad-leaved trees is complex in structure; it is made up 
of different kinds of cells and fibres and lacks the regu- 
larity of arrangement so noticeable in the conifers. This 


difference is so great that in a study of wood structure it 
is best to consider the two kinds separately. 

In this country the great variety of woods, and especially 
of useful woods, often makes the mere distinction of the 
kind or species of tree most difficult. Thus there are at 
least eight pines of the thirty-five native ones in the mar- 
ket, some of which so closely resemble each other in their 
minute structure that one can hardly tell them apart, and 
yet they differ in quality and are often mixed or con- 
founded in the trade. Of the thirty-six oaks, of which 
probably not less than six or eight are marketed, we can 
readily recognize by means of their minute anatomy at 
least two tribes — ■ the white and black oaks. The same 
is true of the eleven kinds of hickory, the six kinds of ash, 
etc., etc. 

The list of names of all trees indigenous to the United 
States, as enumerated by the United States Forest Service, 
is 495 in number, the designation of "tree" being ap- 
plied to all woody plants which produce naturally in their 
native habitat one main, erect stem, bearing a definite 
crown, no matter what size they attain. 

Timber is produced only by the Spermatophyta, or 
seed-bearing plants, which are subdivided into the Gym- 
nosperms (conifers), and Angiosperms (broad-leaved). 
The conifer or cone-bearing tree, to which belong the pines, 
larches, and firs, is one of the three natural orders of Gym- 
nosperms. These are generally classed as "softwoods," 
and are more extensively scattered and more generally 
used than any other class of timber, and are simple and 
regular in structure. The so-called "hardwoods" are 
"Dicotyledons" or broad-leaved trees, a subdivision of 
the Angiosperms. They are generally of slower growth, 
and produce harder timber than the conifers, but not 
necessarily so. Basswood, poplar, sycamore, and some 
of the gums, though classed with the hardwoods, are not 
nearly as hard as some of the pines. 




Examining a smooth cross-section or end face of a well- 
grown log of Georgia pine, we distinguish an envelope of 
reddish, scaly bark, a small, whitish pith at the center, 
and between these the wood in a great number of con- 
centric rings. 

Bark and Pith 

The bark of a pine stem is thickest and roughest near 
the base, decreases rapidly in thickness from one to one- 
half inches at the stump to one-tenth inch near the top 
of the tree, and forms in general about ten to fifteen per 
cent of the entire trunk. The pith is quite thick, usually 
one-eighth to one-fifth inch in southern species, though 
much less so in white pine, and is very thin, one-fifteenth 
to one twenty-fifth inch in cypress, cedar, and larch. 

In woods with a thick pith, the pith is finest at the 
stump, grows rapidly thicker toward the top, and be- 
~comes thinnei' again in the crown and limbs, the first one 
to five rings adjoining TTbehaving similarly. 

What is called the pith was onc6^ the seedling tree, and 
in many of the pines and firs, especially after they have 
been seasoning for a good while, this is distinctly notice- 
able in the center of the log, and detaches itself from the 
siu-rounding wood. 

Sap and Heartwood 

Wood is composed of duramen or heartwood, and al- 
burnum or sapwood, and when dry consists approximately 
of 49 per cent by weight of carbon, 6 per cent of hydrogen, 
44 per cent of oxygen, and 1 per cent of ash, which is fairly 
uniform for all species. The sapwood is the external and 


youngest portion of the tree, and often constitutes a very 
considerable proportion of it. It lies next the bark, and 
after a course of years, sometimes many as m the case ot 
oaks, sometimes few, as in the case of firs, it becomes 
hardened and ultimately forms the duramen or heartwood. 
Sapwood is generally of a white or hght color, almost m- 
variably hghter in color than the heartwood, and is very 
conspicuous in the darker-colored woods, as for instance 
the yellow sapwood of mahogany and simihar colored 
woods, and the reddish brown heartwood; or the yellow 
sapwood of Lignum-vitae and the dark green heartwood. 
Sapwood forms a much larger proportion of some trees 
than others, but being on the outer circumference it always 
forms a large proportion of the timber, and even m sound, 
hard pine will be from 40 per cent to 60 per cent of the 
tree, and in some cases much more. It is really imperfect 
wood while the duramen or heartwood is the perfect wood; 
the heartwood of the mature tree was the sapwood of its 
earlier years. Young trees when cut down are almost 
all sapwood, and practically useless as good, sound timber; 
it is, however, through the sapwood that the life-givmg 
iuices which sustain the tree arise from the soil, and if the 
sapwood be cut through, as is done when girdhng the 
tree quickly dies, as it can derive no further nourishment 
from the soil. Although absolutely necessary to the grow- 
ing tree, sapwood is often objectionable to the user as it 
is the first part to decay. In this sapwood many cells are 
active, store up starch, and otherwise assist m the lite 
processes of the tree, although only the last or outer layer 
of cells forms the growing part, and the true life of the tree 
The duramen or heartwood is the inner, darker part ot 
the log In the heartwood all the cells are lifeless cases, 
and serve only the mechanical function of keeping the 
tree from breaking under its own great weight or from 
being laid low by the winds. The darker color of the 
heartwood is due to infiltration of chemical substances 
into the cell walls, but the cavities of the eels m pme are 
not filled up, as is sometimes believed, nor do their wails 
grow thicker, nor are the walls any more hquified than m 
the sapwood. 


Sapwood varies in width and in the number of rings 
which it contains even in different parts of the same tree. 
The same year's growth which is sapwood in one part of 
a disk may be heartwood in another. Sapwood is widest 
in the main part of the stem and often varies within con- 
siderable hmits and without apparent regularity. Gen- 
erally, it becomes narrower toward the top and in the 
limbs, its width varying with the diameter, and being 
the least in a given disk on the side which has the shortest 
radius. Sapwood of old and stunted pines is composed 
of more rings than that of young and thrifty specimens. 
Thus in a pine two hundred and fifty years old a layer of 
wood or an annual ring does not change from sapwood to 
heartwood until seventy or eighty years after it is formed, 
while in a tree one hundred years old or less it remains 
sapwood only from thirty to sixty years. 

The width of the sapwood varies considerably for dif- 
ferent kinds of pine. It is small for long-leaf and white 
pine and great for loblolly and Norway pines. Occupy- 
ing the peripheral part of the trunk, the proportion which 
it forms of the entire mass of the stem is always great. 
Thus even in old long-leaf pines, the sapwood forms 40 
per cent of the merchantable log, while in the loblolly 
and in all young trees the sapwood forms the bulk of the 

The Annual or Yearly Rings 

The concentric annual or yearly rings which appear on 
the end face of a log are cross-sections of so many thin 
layers of wood. Each such layer forms an envelope around 
its inner neighbor, and is in turn covered by the adjoin- 
ing layer without, so that the whole stem is built up of 
a series of thin, hollow cylinders, or rather cones. 

A new layer of wood is formed each season, covering 
the entire stem, as well as all the living branches. The 
thickness of this layer or the width of the yearly ring 
varies greatly in different trees, and also in different parts 
of the same tree. 

In a normally-grown, thrifty pine log the rings are widest 
near the pith, growing more and more narrow toward 


the bark. Thus the central twenty rings in a disk of an 
old long-leaf pine may each be one-eighth to one-sixth 
inch wide, while the twenty rings next to the bark may 
flvpraffe only one-thirtieth inch. 

In our forest trees, rings of one-half inch m width occur 
only near the center in disks of very thrifty trees, of both 
coifers and hardwoods. One-twelfth mch ■•eP^«««'^t^ g°°d, 
thrifty growth, and the mimmum width of one two hun- 
dred inch is often seen in stunted spruce and pine. The 
average width of rings in well-grown, old white pine will 
yirfrom one-twelfth to one-eighteenth inch, whde ^n the 
slower growing long-leaf pine it may be one twenty-fifth 
to one-thirtieth of an inch. The same layer of wood 
is widest near the stump in very thrifty young trees 
especially if grown in the open park; but m old forest 
tees the sanTe year's growth is wider at the "PPe^ part 
of the tree, being narrowest near the stump and often 
also near the very tip of the stem. Generally the nngs 
are widest near the center, growing narrower toward the 

"""n logs from stunted trees the order is often reversed, 
the interior rings being thin and the outer rings widest. 
Frequently, too, zones or bands of very narrow rings, 
representing unfavorable periods of growth, disturb the 

general regularity. . • i i -+1. +^„k. 

Few trees, even among pines, furmsh a log with truly 
circular cross-section. Usually it is an oval, and at the 
stump commonly quite an irregular figure Moreover, 
even^n very regular or circular disks the pith is rarely m 
the center, and frequently one radius is conspicuously 
longer than its opposite, the width ^^ f ^^^.^^^S^' ^^.^^'^ 
aU being greater on one side than on the other. This is 
nearly always so in the limbs, the lower radius exceedmg 
the upper. In extreme cases, especially m the hmbs, a 
ring is frequently conspicuous on one side, and almost 
or entirely lost to view on the other. Where the rings 
are extremely narrow, the dark portion of the nng is often 
wanting, the color being quite umform and light. Ihe 
greater regularity or irregularity of the annual rings has 
much to do with the technical quahties of the timber. 


Spring- and Summer-Wood 

Examining the rings more closely, it is noticed that 
each ring is made up of an inner, softer, light-colored and 
an outer, or peripheral, firmer and darker-colored portion. 
Being formed in the forepart of the season, the inner, 
light-colored part is termed spring-wood, the outer, darker- 
portioned being the summer-wood of the ring. Since the 
latter is very heavy and firm it deterixiines to a very large 
extent the weight and strength of the wood, and as its 
darker color influences the shade of color of the entire 
piece of wood, this color effect becomes a valuable aid in 
distinguishing heavy and strong from light and soft pine 

In most hard pines, like the long-leaf, the dark summer- 
wood appears as a distinct band, so that the yearly ring 
is composed of two sharply defined bands — an inner, 
the spring- wood, and an outer, the summer-wood. But 
in some cases, even in hard pines, and normally in the 
woods of white pines, the spring-wood passes gradually 
into the darker summer-wood, so that a darkly defined 
line occurs only where the spring-wood of one ring abuts 
against the summer-wood of its neighbor. It is this clearly 
defined line which enables the eye to distinguish even the 
very narrow lines in old pines and spruces. 

In some cases, especially in the trunks of Southern pines, 
and normally on the lower side of pine limbs, there occur 
dark bands of wood in the spring-wood portion of the ring, 
giving rise to false rings, which mislead in a superficial 
counting of rings. In the disks cut from limbs these 
dark bands often occupy the greater part of the ring, and 
appear as "lunes," or sickle-shaped figures. The wood of 
these dark bands is similar to that of the true summer- 
wood. The cells have thick walls, but usually the com- 
pressed or flattened form. Normally, the summer-wood 
forms a greater proportion of the rings in the part of the 
tree formed during the period of thriftiest growth. In 
an old tree this proportion is very small in the first two 
to five rings about the pith, and also in the part next to 
the bark, the intermediate part showing a greater pro- 



portion of summer-wood. It is also greatest in a disk 
taken from near the stump, and decreases upward in the 
stem, thus fully accounting for the difference in weight 
and firmness of the wood of these different parts. 

In the long-leaf pine the summer-wood often forms 
scarcely ten per cent of the wood in the central five rings; 
forty to fifty per cent of the next one hundred rings, about 
thirty per cent of the next fifty, and only about twenty 
per cent in the fifty 
rings next to the 
bark. It averages 
forty-five per cent of 
the wood of the 
stump and only 
twenty-four per cent 
of that of the top. 

Sawing the log into 
boards, the yearly 
rings are represented 
on the board faces 
of the middle board 
(radial sections) by 
narrow parallel strips 
(see Fig. 1), an in- 
ner, lighter stripe 
and its outer, darker 
neighbor always cor- 
responding to one 
annual ring. 

On the faces of the 
boards nearest the slab (tangential or bastard boards) the 
several years' growth should also appear as parallel, but 
much broader stripes. This they do if the log is short 
and very perfect. Usually a variety of pleasing patterns 
is displayed on the boards, depending on the position of 
the saw cut and on the regularity of growth of the log 
(see Fig. 1). Where the cut passes through a prominence 
(bump or crook) of the log, irregular, concentric circlets 
and ovals are produced, and on almost all tangent boards 
arrow or V-shaped forms occur. 

Fig. 1. Board of Pine. CS, cross-section; RS, 
radial section; TS, tangential section; 
sw, summer-wood; spw, spring-wood. 



Anatomical Structure 

Holding a well-smoothed disk or cross-section one- 
eighth inch thick toward the light, it is readily seen that 
pine wood is a very porous structure. If viewed with a 
strong magnifier, the little tubes, especially in the spring- 
wood of the rings, are easily distinguished, and their ar- 
rangement in regular, straight, radial rows is apparent. 
Scattered through the summer-wood portion of the 
rings, numerous irregular grayish dots (the resin ducts) 

disturb the uniform- 
ity and regularity of 
the structure. Mag- 
nified one hundred 
times, a piece of 
spruce, which is sim- 
ilar to pine, presents 
a picture like that 
shown in Fig. 2. 
Only short pieces of 
the tubes or cells of 
which the wood is 
composed are repre- 
sented in the picture. 
The total length of 
these fibres is from 
one-twentieth to one- 
fifth inch, being the 
smallest near the 
pith, and is fifty to 
one hundred times 
as great as their 
width (see Fig. 3). 
They are tapered and closed at their ends, polygonal or 
rounded and thin-walled, with large cavity, lumen or in- 
ternal space in the spring-wood, and thick-walled and 
flattened radially, with the internal space or lumen much 
reduced in the summer-wood (see right-hand portion 
of Fig. 2). This flattening, together with the thicker walls 
of the cells, which reduces the lumen, causes the greater 


2. Wood of Spruce. 1, natural size; 2, 
small part of one ring magnified 100 
times. The vertical tubes are wood 
fibres, in this case all "tracheids." to, 
medullary or pith ray; n, transverse 
tracheids of ray; a, b, and c, bordered 
pits of the tracheids, more enlarged. 



firmness and darker color of the summer-wood. There 
is more material in the same volume. As shown in the 
figure, the tubes, cells or "tracheids" are decorated on 
their walls by circlet-like structures, the "bordered pits," 
sections of which are seen more magnified as a, b, and c, 
Fig. 2. These pits are in the nature of pores, covered 
by very thin membranes, and serve as water- 
ways between the cells or tracheids. The dark 
lines on the side of the smaller piece (1, Fig. 2) 
appear when magnified (in 2, Fig. 2) as tiers 
of eight to ten rows of cells, which run radially 
(parallel to the rows of tubes or tracheids), 
and are seen as bands on the radial face and 
as rows of pores on the tangential face. These 
bands or tiers of cell rows are the medullary 
rays or pith rays, and are common to all our 
lumber woods. 

In the pines and other conifers they are quite 
small, but they can readily be seen even with- 
out a magnifier. If a radial surface of split- 
wood (not smoothed) is examined, the entire 
radial face will be seen almost covered with 
these tiny structures, which appear as fine but 
conspicuous cross-lines. As shown in Fig. 2, the 
cells of the medullary or pith are smaller and 
very much shorter than the wood fibre or 
tracheids, and their long axis is at right angles 
to that of the fiber. 

In pines and spruces the cells of the upper 
and lower rows of each tier or pith ray have 
"bordered" pits, like those of the wood fibre 
or tracheids proper, but the cells of the inter- 
mediate rows in the rays of cedars, etc., have 
only "simple" pits, i.e., pits devoid of the 
saucer-like ''border" or rim. In pine, many 
of the pith rays are larger than the majority, 

Fig. 3. Group of Fibres from Pine Wood. Partly schematic. The httle 
circles are "border pits" (see Fig. 2, a-c). The transverse rows of 
square pits indicate the places of contact of these fibres and the cells 
of the neighboring pith rays. Magnified about 25 times. 


each containing a whitish hne, the horizontal resin duct, 
which, though much smaller, resembles the vertical ducts 
on the cross-section. The larger vertical resin ducts are 
best observed on removal of the bark from a fresh piece 
of white pine cut in the winter where they appear as con- 
spicuous white lines, extending often for many inches up 
and down the stem. Neither the horizontal nor the verti- 
cal resin ducts are vessels or cells, but are openings between 
cells, i.e., intercellular spaces, in which the resin accumu- 
lates, freely oozing out when the ducts of a fresh piece of 
sapwood are cut. They are present only in our coniferous 
woods, and even here they are restricted to pine, spruce, 
and larch, and are normally absent in fir, cedar, cypress, 
and yew. Altogether, the structure of coniferous woods 
is very simple and regular, the bulk being made up of the 
small fibres called tracheids, the disturbing elements of 
pith rays and resin ducts being insignificant, and hence 
the great uniformity and great technical value of conifer- 
ous woods. 



Light, soft, stiff, not strong, of fine texture. Sap- and 
heartwood distinct, the former Hghter, the latter a dull 
grayish brown or red. The wood seasons rapidly, shrinks 
and checks but little, and is very durable in contact with 
the soil. Used like soft pine, but owing to its great dura- 
bility preferred for shingles, etc. Cedars usually occur 
scattered, but they form in certain localities forests of 
considerable extent. 

(a) White Cedars 

1. White Cedar {Thuya occidentalis) (Arborvitse, Tree of 

Life). Heartwood light yellowish brown, sap wood 
nearly white. Wood light, soft, not strong, of fine 
texture, very durable in contact with the soil, very 
fragrant. Scattered along streams and lakes, fre- 
quently covering extensive swamps; rarely large 
enough for lumber, but commonly used for fence 
posts, rails, railway ties, and shingles. This species 
has been extensively cultivated as an ornamental tree 
for at least a century. Maine to Minnesota and 

2. Canoe Cedar (Thuya gigantea) (Red Cedar of the West). 

In Oregon and Washington a very large tree, cover- 
ing extensive swamps; in the mountains much smaller, 
skirting the water courses. An important lumber 
tree. The wood takes a fine polish; suitable for 
interior finishing, as there is much variety of shading 
in the color. Washington to northern California 
and eastward to Montana. 

3. White Cedar (Chamcecyparis thyoides). Medium-sized 

tree. Heartwood light brown with rose tinge, sap- 


wood paler. Wood light, soft, not strong, close- 
grained, easily worked, very durable in contact with 
the soil and very fragrant. Used in boatbuilding, 
cooperage, interior finish, fence posts, railway ties, 
etc. Along the coast from Maine to Mississippi. 

4. "White Cedar (Chamcecyparis Lawsoniana) (Port Or- 

ford Cedar, Oregan Cedar, Lawson's Cypress, Ginger 
Pine). A very large tree. A fine, close-grained, 
yellowish-white, durable timber, elastic, easily worked, 
free of knots, and fragrant. Extensively cut for 
lumber; heavier and stronger than any of the pre- 
ceding. Along the coast line of Oregon. 

5. White Cedar {Libocedrus decurrens) (Incense Cedar). 

A large tree, abundantly scattered among pine and 
fir. Wood fine-grained. Cascades and Sierra Nevada 
Mountains of Oregon and California. 

6. Yellow Cedar (Cupressus nootkatensis) (Alaska Cedar, 

Alaska Cypress). A very large tree, much used for 
panelling and furniture. A fine, close-grained, yel- 
lowish white, durable timber, easily worked. Along 
the coast line of Oregon north. 

(&) Red Cedars 

7. Red Cedar {Juniperus Virginiana) (Savin Juniper, 

Juniper, Red Juniper, Juniper Bush, Pencil Cedar). 
Heartwood dull red color, thin sapwood nearly white. 
Close even grain, compact structure. Wood light, 
soft, weak, brittle, easily worked, durable in contact 
with the soil, and fragrant. Used for ties, posts, 
interior finish, pencil cases, cigar boxes, silos, tanks, 
and especially for lead pencils, for which purpose 
alone several million feet are cut each year. A small 
to medium-sized tree scattered through the forests, 
or in the West sparsely covering extensive areas (cedar 
brakes) . The red cedar is the most widely distributed 
conifer of the United States, occurring from the At- 
lantic to the Pacific, and from Florida to Minnesota. 


Attains a suitable size for lumber only in the Southern, 
and more especially the Gulf States. 

8. Red Cedar (Juniperus communis) (Ground Cedar). 

Small-sized tree, its maximum height being about 
25 feet. It is found widely distributed throughout 
the Northern hemisphere. Wood in its quality similar 
to the preceding. The fruit of this species is gathered 
in large quantities and used in the manufacture of 
gin; whose peculiar flavor and medicinal properties 
are due to the oil of Juniper berries, which is secured 
by adding the crushed fruit to undistilled grain spirit, 
or by allowing the vapor to pass over it before con- 
densation. Used locally for construction purposes, 
fence posts, etc. Ranges from Greenland to Alaska, 
in the East, southward to Pennsylvania and northern 
Nebraska; in the Rocky Mountains to Texas, Mexico, 
and Arizona. 

9. Redwood {Sequoia sempervirens) (Sequoia, California 

Redwood, Coast Redwood). Wood in its quality 
and uses like white cedar. Thick, red heartwood, 
changing to reddish brown when seasoned. Thin 
sapwood, nearly white, coarse, straight grain, com- 
pact structure. Light, not strong, soft, very durable in 
contact with the soil, not resinous, easily worked, 
does not burn easily, receives high polish. Used for 
timber, shingles, flumes, fence posts, cofflns, railway ties, 
water pipes, interior decorations, and cabinetmaking. 
A very large tree, limited to the coast ranges of Cali- 
fornia, and forming considerable forests, which are 
rapidly being converted into lumber. 


10. Cypress (Taxodium distinchum) (Bald Cypress, Black, 
White, and Red Cypress, Pecky Cypress). Wood in 
its appearance, quality, and uses similar to white 
cedar. "Black" and "White Cypress" are heavy 
and light forms of the same species. Heartwood 
brownish; sapwood nearly white. Wood close, 


straight-grain, frequently full of small holes caused by- 
disease known as "pecky cypress." Greasy ap- 
pearance and feeling. Wood light, soft, not strong, 
durable in contact with the soil, takes a fine polish. 
Green wood often very heavy. Used for carpentry, 
building construction, shingles, cooperage, railway 
ties, silos, tanks, vehicles, and washing machines. 
The cypress is a large, deciduous tree, inhabiting 
swampy lands, and along rivers and coasts of the 
Southern parts of the United States. Grows to a 
height of 150 feet and 12 feet in diameter. 


This name is frequently applied to wood and to trees 
which are not fir; most commonly to spruce, but also, 
especially in English markets, to pine. It resembles 
spruce, but is easily distinguished from it, as well as from 
pine and larch, by the absence of resin ducts. Quality, 
uses, and habits similar to spruce. 

11. Balsam Fir (Ahies balsamea) (Balsam, Fir Tree, Balm 
of Gilead Fir). Heartwood white to brownish; sap- 
wood lighter color; coarse-grained, compact structure, 
satiny. Wood light, not durable or strong, resinous, 
easily split. Used for boxes, crates, doors, millwork, 
cheap lumber, paper pulp. Inferior to white pine 
or spruce, yet often mixed and sold with these species 
in the lumber market. A medium-sized tree scattered 
throughout the northern pineries, and cut in lumber 
operations whenever of sufficient size. Minnesota 
to Maine and northward. 

12. White Fir {Ahies grandis and Ahies concolor). Medium- 
to very large-sized tree, forming an important part of 
most of the Western mountain forests, and furnishes 
much of the lumber of the respective regions. The 
former occurs from Vancouver to California, and the 
latter from Oregon to Aj-izona and eastward to Colo- 
rado and Mexico. The wood is soft and light, coarse- 
grained, not unlike the "Swiss pine" of Europe, but 


darker and firmer, and is not suitable for any purpose 
requiring strength. It is used for boxes,, barrels, and 
to a small extent for wood pulp. 

13. "White Fir {Abies amabalis). Good-sized tree, often 
forming extensive mountain forests. Wood similar 
in quality and uses to Abies grandis. Cascade Moun- 
tains of Washington and Oregon. 

14. Red Fir (Abies nobilis) (Noble Fir) (not to be con- 
founded with Douglas spruce. See No. 40). Large 
to very large-sized tree, forming extensive forests on 
the slope of the mountains between 3,000 and 4,000 
feet elevation. Cascade Mountains of Oregon. 

15. Red Fir {Abies magnifica). Very large-sized tree, 
forming forests about the base of Mount Shasta. 
Sierra Nevada Mountains of California, from Mount 
Shasta southward. 


Light to medium weight, soft, stiff, but brittle, commonly 
cross-grained, rough and splintery. Sapwood and heart- 
wood not well defined. The wood of a light reddish-gray 
color, free from resin ducts, moderately durable, shrinks 
and warps considerably in drying, wears rough, retains 
nails firmly. Used principally for dimension stuff and 
timbers. Hemlocks are medium- to large-sized trees, 
commonly scattered among broad-leaved trees and coni- 
fers, but often forming forests of almost pure growth. 

16. Hemlock {Tsuga canadensis) (Hemlock Spruce, 
Peruche). Medium-sized tree, furnishes almost all 
the hemlock of the Eastern market. Maine to Wis- 
consin, also following the Alleghanies southward to 
Georgia and Alabama. 

17. Hemlock {Tsuga mertensiana) . Large-sized tree, 
wood claimed to be heavier and harder than the 
Eastern species and of superior quality. Used for 
pulp wood, floors, panels, and newels. It is not 


suitable for heavy construction, especially where ex- 
posed to the weather, it is straight in grain and will 
take a good polish. Not adapted for use partly in 
and partly out of the ground; in fresh water as piles 
will last about ten years, but as it is softer than fir 
it is less able to stand driving successfully. Wash- 
ington to California and eastward to Montana. 


Wood like the best of hard pine both in appearance, 
quality, and uses, and owing to its great durability some- 
what preferred in shipbuilding, for telegraph poles, and 
railway ties. In its structure it resembles spruce. The 
larches are deciduous trees, occasionally covering con- 
siderable areas, but usually scattered among other conifers. 

18. Tamarack {Larix laricina var. Americana) (Larch, 
Black Larch, American Larch, Hacmatac). Heart- 
wood light brown in color, sapwood nearly white, 
coarse conspicuous grain, compact structure, annual 
rings pronounced. Wood heavy, hard, very strong, 
durable in contact with the soil. Used for railway 
ties, fence posts, sills, ship timbers, telegraph poles, 
flagstaffs. Medium-sized tree, often covering swamps, 
in which case it is smaller and of poor quality. Maine 
to Minnesota, and southward to Pennsylvania. 

19. Tamarack (Larix occidentalis) (Western Larch, Larch). 
Large-sized trees, scattered, locally abundant. Is 
little inferior to oak in strength and durability. 
Heartwood of a light brown color with lighter sap- 
wood, has a fine, slightly satiny grain, and is 
fairly free from knots; the annual rings are distant. 
Used for railway ties and shipbuilding. Washington 
and Oregon to Montana. 


Very variable, very light and soft in ''soft" pine, such 
as white pine; of medium weight to heavy and quite 
hard in "hard" pine, of which the long-leaf or Georgia 


pine is the extreme form. Usually it is stiff, quite strong, 
of even texture, and more or less resinous. The sapwood 
is yellowish white; the heartwood orange brown. Pine 
shrinks moderately, seasons rapidly and without much 
injury; it works easily, is never too hard to nail (unlike 
oak or hickory); it is mostly quite durable when in con- 
tact with the soil, and if well seasoned is not subject to 
the attacks of boring insects. The heavier the wood, the 
darker, stronger, and harder it is, and the more it shrinks 
and checks when seasoning. Pine is used more exten- 
sively than any other wood. It is the principal wood in 
carpentry, as well as in all heavy construction, bridges, 
trestles, etc. It is also used in almost every other wood 
industry; for spars, masts, planks, and timbers in ship- 
building, in car and wagon construction, in cooperage and 
woodenware; for crates and boxes, in furniture work, for 
toys and patterns, water pipes, excelsior, etc. Pines are 
usually large-sized trees with few branches, the straight, 
cyhndrical, useful stem forming by far the greatest part 
of the tree. They occur gregariously, forming vast forests, 
a fact which greatly facilitates their exploitation. Of the 
many special terms appUed to pine as lumber, denoting 
sometimes differences in quality, the following deserve 
attention: "White pine/' ''pumpkin pine," "soft pine," 
in the Eastern markets refer to the wood of the white 
pine {Pinus strohus), and on the Pacific Coast to that of 
the sugar pine (Pinus lambertina) . "Yellow pine" is 
apphed in the trade to all the Southern lumber pines; in 
the Northwest it is also apphed to the pitch pine (Pinus 
regida) ; in the West it refers mostly to the bull pine (Pinus 
ponder osa). "Yellow long-leaf pine" (Georgia pine), 
chiefly used in advertisements, refers to the long-leaf 
pine (Pinus palustris). 

(a) Soft Pines 

20. White Pine (Pinus strohus) (Soft Pine, Pumpkin Pine, 
Weymouth Pine, Yellow Deal). Large to very large- 
sized tree, reaching a height of 80 to 100 feet or more, 
and in some instances 7 or 8 feet in diameter. For 
the last fifty years the most important timber treo 


of the United States, furnishing the best quahty of 
soft pine. Heartwood cream white; sap wood nearly- 
white. Close straight grain, compact structure; com- 
paratively free from knots and resin. Soft, uniform; 
seasons well; easy to work; nails without splitting; 
fairly durable in contact with the soil; and shrinks 
less than other species of pine. Paints well. Used 
for carpentry, construction, building, spars, masts, 
matches, boxes, etc., etc., etc. 

21. Sugar Pine (Pinus lambertiana) (White Pine, Pump- 
kin Pine, Soft Pine). A very large tree, forming ex- 
tensive forests in the Rocky Mountains and furnishing 
most of the timber of the western United States. It 
is confined to Oregon and California, and grows at 
from 1,500 to 8,000 feet above sea level. Has an 
average height of 150 to 175 feet and a diameter of 
4 to 5 feet, with a maximum height of 235 feet and 12 
feet in diameter. The wood is soft, durable, straight- 
grained, easily worked, very resinous, and has a 
satiny luster which makes ft appreciated for interior 
work. It is extensively used for doors, blinds, sashes, 
and interior finish, also for druggists' drawers, owing 
to its freedom from odor, for oars, mouldings, ship- 
building, cooperage, shingles, and fruit boxes. Oregon 
and California. 

22. White Pine (Pinus monticolo). A large tree, at home 
in Montana, Idaho, and the Pacific States. Most 
common and locally used in northern Idaho. 

23. White Pine (Pinus flexilis). A small-sized tree, 
forming mountain forests of considerable extent and 
locally used. Eastern Rocky Mountain slopes, Mon- 
tana to New Mexico. 

(b) Hard Pines 

24. Long-Leaf Pine (Pinus palustris) (Georgia Pine, 
Southern Pine, Yellow Pine, Southern Hard Pine, 
Long-straw Pine, etc.). Large-sized tree. This 
species furnishes the hardest and most durable as 


well as one of the strongest pine timbers in the market. 
Heartwood orange, sapwood lighter color, the annual 
rings are strongly marked, and it is full of resinous 
matter, making it very durable, but difficult to work. 
It is hard, dense, and strong, fairly free from knots, 
straight-grained, and one of the best timbers for 
heavy engineering work where great strength, long 
span, and durability are required. Used for heavy 
construction, shipbuilding, cars, docks, beams, ties, 
flooring, and interior decoration. Coast region from 
North Carolina to Texas. 

25. Bull Pine (Pinus ponder osa) (Yellow Pine, Western 
Yellow Pine, Western Pine, Western White Pine, 
California White Pine). Medium- to very large- 
sized tree, forming extensive forests in the Pacific and 
Rocky Mountain regions. Heartwood reddish brown, 
sapwood yellowish white, and there is often a good 
deal of it. The resinous smell of the wood is very 
remarkable. It is extensively used for beams, floor- 
ing, ceilings, and building work generally. 

26. Bull Pine (Pinus Jeffreyi) (Black Pine). Large- 
sized tree, wood resembles Pinus ponderosa and re- 
placing same at high altitudes. Used locally in 

27. Loblolly Pine (Pinus tceda) (Slash Pine, Old Field 
Pine, Rosemary Pine, Sap Pine, Short-straw Pine). 
A large-sized tree, forms extensive forests. Wider- 
ringed, coarser, lighter, softer, with more sapwood 
than the long-leaf pine, but the two are often con- 
founded in the market. The more Northern tree 
produces lumber which is weak, brittle, coarse-grained, 
and not durable, the Southern tree produces a better 
quality wood. Both are very resinous. This is the 
common lumber pine from Virginia to South Caro- 
lina, and is found extensively in Arkansas and Texas. 
Southern States, Virginia to Texas and Arkansas. 

28. Norway Pine (Pinus resinosa) (American Red Pine, 
Canadian Pine). Large-sized tree, never forming 


forests, usually scattered or in small groves, together 
with white pine. Largely sapwood and hence not 
durable. Heartwood reddish white, with fine, clear 
grain, fairly tough and elastic, not liable to warp and 
split. Used for building construction, bridges, piles, 
masts, and spars. Minnesota to Michigan; also in 
New England to Pennsylvania. 

29. Short-Leaf Pine {Pinus echinata) (Slash Pine, Spruce 
Pine, Carolina Pine, Yellow Pine, Old Field Pine, 
Hard Pine). A medium- to large-sized tree, resem- 
bling loblolly pine, often approaches in its wood the 
Norway pine. Heartwood orange, sapwood lighter; 
compact structure, apt to be variable in appearance 
in cross-section. Wood usually hard, tough, strong, 
durable, resinous. A valuable timber tree, sometimes 
worked for turpentine. Used for heavy construction, 
shipbuilding, cars, docks, beams, ties, flooring, and 
house trim. Pinus echinata, palustris, and tmda are 
very similar in character, of thin wood and very dif- 
ficult to distinguish one from another. As a rule, how- 
ever, palustris (Long-leaf Pine) has the smallest and 
most uniform growth rings, and Pinus tceda (Loblolly 
Pine) has the largest. All are apt to be bunched 
together in the lumber market as Southern Hard 
Pine. All are used for the same purposes. Short- 
leaf is the common lumber pine of Missouri and 
Arkansas. North Carolina to Texas and Missouri. 

30. Cuban Pine (Pinus cubensis) (Slash Pine, Swamp 
Pine, Bastard Pine, Meadow Pine). Resembles long- 
leaf pine, but commonly has a wider sapwood and 
coarser grain. Does not enter the markets to any 
extent. Along the coast from South Carolina to 

31. Pitch Pine (Pinus rigida) (Torch Pine). A small to 
medium-sized tree. Heartwood light brown or red, 
sapwood yellowish white. Wood light, soft, not 
strong, coarse-grained, durable, very resinous. Used 
locally for lumber, fuel, and charcoal. Coast regions 


from New York to Georgia, and along the mountains 
to Kentucky. 

32. Black Pine (Pinus murryana) (Lodge-pole Pine, 
Tamarack). Small-sized tree. Rocky Mountains 
and Pacific regions. 

33. Jersey Pine (Pinus inops var. Virginiana) (Scrub 
Pine). Small-sized tree. Along the coast from New 
York to Georgia and along the mountains to Kentucky. 

34. Gray Pine {Pinus divaricata var. banksiana) (Scrub 
Pine, Jack Pine). Medium- to large-sized tree. 
Heartwood pale brown, rarely yellow; sap wood nearly 
white. Wood fight, soft, not strong, close-grained. 
Used for fuel, rafiway ties, and fence posts. In days 
gone by the Indians preferred this species for frames 
of canoes. Maine, Vermont, and Michigian to Min- 

REDWOOD (See Cedar) 


Resembles soft pine, is fight, very soft, stiff, moderately 
strong, less resinous than pine; has no distinct heartwood, 
and is of whitish color. Used fike soft pine, but also em- 
ployed as resonance wood in musical instruments and 
preferred for paper pulp. Spruces, fike pines, form ex- 
tensive forests. They are more frugal, thrive on thinner 
soils, and bear more shade, but usuafiy require a more 
humid climate. "Black" and "White" spruce as appfied 
by lumbermen usually refer to narrow and wide-ringed 
forms of black spruce {Picea nigra). 

35. Black Spruce (Picea nigra var. mariana). Medium- 
sized tree, forms extensive forests in northwestern 
United States and in British America; occurs scat- 
tered or in groves, especially in low lands throughout 
the northern pineries. Important lumber tree in 
eastern United States. Heartwood pale, often with 
reddish tinge; sap wood pure white. Wood light, 


soft, not strong. Chiefly used for manufacture of 
paper pulp, and great quantities of this as well as 
Picea alba are used for this purpose. Used also for 
sounding boards for pianos, violins, etc. Maine to 
Minnesota, British America, and in the Alleghanies 
to North Carolina. 

36. White Spruce (Picea canadensis yar. alba). Medium- 
to large-sized tree. Heartwood light yellow; sap- 
wood nearly white. Generally associated with the 
preceding. Most abundant along streams and lakes, 
grows largest in Montana and forms the most im- 
portant tree of the sub-arctic forest of British America. 
Used largely for floors, joists, doors, sashes, mouldings, 
and panel work, rapidly superceding Pinus strobus 
for building purposes. It is very similar to Norway 
pine, excels it in toughness, is rather less durable and 
dense, and more liable to warp in seasoning. Northern 
United States from Maine to Minnesota, also from 
Montana to Pacific, British America. 

37. White Sprace (Picea engelmanni). Medium- to large- 
sized tree, forming extensive forests at elevations 
from 5,000 to 10,000 feet above sea level; resembles 
the preceding, but occupies a different station. A 
very important timber tree in the central and southern 
parts of the Rocky Mountains. Rocky Mountains 
from Mexico to Montana. 

38. Tide -Land Spruce (Picea sitchensis) (Sitka Spruce). 
A large-sized tree, forming an extensive coast-belt 
forest. Used extensively for all classes of cooperage 
and woodenware on the Pacific Coast. Along the 
sea-coast from Alaska to central California. 

39. Red Spruce (Picea rubens). Medium-sized tree, gen- 
erally associated with Picea nigra and occurs scattered 
throughout the northern pineries. Heartwood red- 
dish; sap wood lighter color, straight-grained, com- 
pact structure. Wood light, soft, not strong, elastic, 
resonant, not durable when exposed. Used for floor- 
ing, carpentry, shipbuilding, piles, posts, railway 


ties, paddles, oars, sounding boards, paper pulp, and 
musical instruments. Montana to Pacific, British 


Spruce or fir in name, but resembling hard pine or larch 
in appearance, quality and uses of its wood. 

40. Douglas Spruce (Pseudotsuga douglasii) (Yellow Fir, 
Red Fir, Oregon Pine). One of the most important 
trees of the western United States; grows very large 
in the Pacific States, to fair size in all parts of the 
mountains, in Colorado up to about 10,000 feet above 
sea level; forms extensive forests, often of pure 
growth, it is really neither a pine nor a fir. Wood 
very variable, usually coarse-grained and heavy, 
with very pronounced summer-wood. Hard and 
strong (''red" fir), but often fine-grained and light 
("yellow" fir). It is the chief tree of Washington 
and Oregon, and most abundant and most valuable 
in British Columbia, where it attains its greatest 
size. From the plains to the Pacific Ocean, and from 
Mexico to British Columbia. 

41. Red Fir {Pseudotsuga taxifolia) (Oregon Pine, Puget 
Sound Pine, Yellow Fir, Douglas Spruce, Red Pine). 
Heartwood light red or yellow in color, sapwood nar- 
row, nearly white, comparatively free from resins, vari- 
able annual rings. Wood usually hard, strong, difficult 
to work, durable, splinters easily. Used for heavy 
construction, dimension timber, railway ties, doors, 
blinds, interior finish, piles, etc. One of the most 
important of Western trees. From the plains to 
the Pacific Ocean, and from Mexico to British America. 

TAMARACK (See Larch) 


Wood heavy, hard, extremely stiff and strong, of fine 
texture with a pale yellow sapwood, and an orange-red 
heartwood; seasons well and is quite durable. Exten- 


sively used for archery bows, turner's ware, etc. The 
yews form no forests, but occur scattered with other 

42. Yew {Taxus brevifolia). A small to medium-sized 
tree of the Pacific region. 




On a cross-section of oak, the same arrangement of pith 
and bark, of sapwood and heartwood, and the same dis- 
position of the wood in well-defined concentric or annual 
rings occur, but the rings are marked by Hnes or rows of 
conspicuous pores or openings, which occupy the greater 
part of the spring-wood for each ring (see Fig. 4, also 6), 
and are, in fact the hollows of vessels 
through which the cut has been 
made. On the radial section or 
quarter-sawn board the several 
layers appear as so many stripes 
(see Fig. 5); on the tangential sec- 
tion or "bastard" face patterns 
similar to those mentioned for pine 
wood are observed. But while the 
patterns in hard pine are marked 
by the darker summer-wood, and ^. . ^, , , ^ , ^^ 

•^ 1 ,. 1 • M. J.- Fig. 4. Block of Oak. CS, 

are composed of plam, alternatmg cross-section; RS, 

stripes of darker and hghter wood, - ^ • -^ ■ 

the figures in oak (and other broad- 
leaved woods) are due chiefly to 
the vessels, those of the spring- 
wood in oak being the most 

conspicuous (see Fig. 5). So that in an oak table, the 
darker, shaded parts are the spring-wood, the hghter 
unicolored parts the summer-wood. On closer examina- 
tion of the smooth cross-section of oak, the spring-wood 
part of the ring is found to be formed in great part 
of pores; large, round, or oval openings made by the cut 
through long vessels. These are separated by a grayish 

radial section; TS, tan- 
gential section; mr, 
medullary or pith ray; 
a, height; h, width; and 
e, length of pith ray. 







Fig. 5. Board of Oak. CS, cross-section; RS, radial section; TS, tangential 
section; v, vessels or pores, cut through; A, slight curve in log which 
appears in section as an islet. 

Fig. 6. Cross-section of Oak (Magnified about 5 times). 



and quite porous tissue (see Fig. 6, A), which continues 
here and there in the form of radial, often branched, 
patches (not the pith rays) into and through the summer- 
wood to the spring-wood of the next ring. The large 
vessels of the spring-wood, occupying six to ten per cent 
of the volume of a log in very good oak, and twenty-five 
per cent or more in inferior and narrow-ringed timber, 
are a very important feature, since it is evident that the 
greater their share in the volume, the lighter and weaker 
the wood. They are smallest near the pith, and grow 
wider outward. They are wider in the stem than hmb, 
and seem to be of indefinite length, forming open channels, 
in some cases probably as long 
as the tree itself. Scattered 
through the radiating gray 
patches of porous wood are 
vessels similar to those of the 
spring-wood, but decidedly 
smaher. These vessels are 
usually fewer and larger near 
the outer portions of the ring. 
Their number and size can be 
utilized to distinguish the oaks 
classed as white oaks from 
those classed as black and 
red oaks. They are fewer and 
larger in red oaks, smaller but 
much more numerous in white 
oaks. The summer-wood, 
except for these radial, grayish patches, is dark colored and 
firm. This firm portion, divided into bodies or strands by 
these patches of porous wood, and also by fine, wavy, concen- 
tric lines of short, thin-walled cells (see Fig. 6, A), consists 
of thin-walled fibres (see Fig. 7, B), and is the chief ele- 
ment of strength in oak wood. In good white oak it forms 
one-half or more of the wood, if it cuts Uke horn, and the 
cut surface is shiny, and of a deep chocolate brown color. 
In very narrow-ringed wood and in inferior red oak it is 
usually much reduced in quantity as well as quality. The 
pith rays of the oak, unlike those of the coniferous woods, 

Fig. 7. Portion of the Firm Bodies 
of Fibres with Two Cells of a 
Small Pith Ray mr (Highly 



are at least in part very large and conspicuous. (See Fig. 
4; their height indicated by the letter a, and their width 
by the letter 6.) The large medullary rays of oak are 
often twenty and more cells wide, and several hundred 

cell rows in height, which amount 
commonly to one or more inches. 
These large rays are conspicuous 
on all sections. They appear as 
long, sharp, grayish lines on the 
cross-sections; as short, thick lines, 
tapering at each end, on the tan- 
gential or "bastard" face, and as 
broad, shiny bands, "the mirrors," 
on the radial section. In addition 
to these coarse rays, there is also 
a large number of small pith rays, 
which can be seen only when mag- 
nified. On the whole, the pith 
rays form a much larger part of 
the wood than might be supposed. 
In specimens of good white oak it 
has been found that they form 
about sixteen to twenty-five per 
cent of the wood. 

Minute Structure 

If a well-smoothed thin disk or 
cross-section of oak (say one-six- 
teenth inch thick) is held up to 
the light, it looks very much like 
a sieve, the pores or vessels ap- 
pearing as clean-cut holes. The 
c, a single joint or cell of spring-wood and gray patches are 
LdlngSnto ItTZler ^^eu to be quite porous, but the 
and lower neighbors; d, firm bodies of fibres between them 
tracheid; e, wood fibre are dense and opaque. Examined 
^^^^^^- with a magnifier it will be noticed 

that there is no such regularity of arrangement in straight 
rows as is conspicuous in pine. On the contrary, great 
irregularity prevails. At the same time, while the pores 

Fig. 8. Isolated Fibres and 
Cells, a, four cells of 
wood, parenchyma; b, 
two cells from a pith ray; 


are as large as, pin holes, the cells of the denser wood, 
unlike those of pine wood, are too small to be distin- 
guished. Studied with the microscope, each vessel is 
found to be a vertical row of a great number of short, 
wide tubes, joined end to end (see Fig. 8, c). The 
porous spring-wood and radial gray tracts are partly 
composed of smaller vessels, but chiefly of tr,acheids, like 
those of pine, and of shorter cells, the "wood parenchyma," 
resembling the cells of the medullary rays. These latter, 

Fig. 9. Cross-section of Basswood (Magnified), v, vessels; mr, pith rays. 

as well as the fine concentric lines mentioned as occurring 
in the summer-wood, are composed entirely of short tube- 
like parenchyma cells, with square or oblique ends (see 
Fig. 8, a and h). The wood fibres proper, which form the 
dark, firm bodies referred to, are very fine, thread-like 
cells, one twenty-fifth to one-tenth inch long, with a wall 
commonly so thick that scarcely any empty internal space 
or lumen remains (see Figs, 8, e, and 7, B). If, in- 
stead of oak, a piece of poplar or basswood (see Fig. 9) 
had been used in this study, the structure would have 
been found to be quite different. The same kinds of cell- 
elements, vessels, etc., are, to be sure, present, but their 
combination and arrangement are different, and thus 
from the great variety of possible combinations results 
the great variety of structure and, in consequence, of 
the qualities which distinguish the wood of broad-leaved 
trees. The sharp distinction of sapwood and heartwood 
is wanting; the rings are not so clearly defined; the vessels 


of the wood are small, very numerous, and rather evenly 
scattered through the wood of the annual rmgs, so that 
the distinction of the ring almost vanishes and the medul- 
lary or pith rays in poplar can be seen, without bemg 
magnified, only on the radial section. 


Woods of complex and very variable structure, and 
therefore differing widely in quality, behavior, and con- 
sequently in applicability to the arts. 


1. Ailanthus {Ailanthus glandulosa). Medium to large- 

sized tree. Wood pale yellow, hard, fine-grained, and 
satiny. This species originally came from China, 
where it is known as the Tree of "Heaven," was in- 
troduced into the United States and planted near 
Philadelphia during the 18th century, and is more 
ornamental than useful. It is used to some extent 
in cabinet work. Western Pennsylvania and Long 
Island, New York. 


Wood heavy, hard, stiff, quite tough, not durable in 
contact with the soil, straight-grained, rough on the split 
surfaces and coarse in texture. The wood shrinks moder- 
ately, seasons with little injury, stands well, and takes a 
good polish. In carpentry, ash is used for stairways, 
panels, etc. It is used in shipbuilding, in the construction 
of cars, wagons, etc., in the manufacture of all kinds of 
farm implements, machinery, and especially of all kinds 
of furniture; for cooperage, baskets, oars, tool handles, 
hoops, etc., etc. The trees of the several species of ash 
are rapid growers, of small to medium height with stout 
trunks. They form no forests, but occur scattered in 
almost all our broad-leaved forests. 

2. White Ash (Fraxinus Americana). Medium-, some- 

times large-sized tree. Heartwood reddish brown, 
usually mottled; sap wood lighter color, nearly white. 
Wood heavy, hard, tough, elastic, coarse-grained, 


compact structure. Annual rings clearly marked by 
large open pores, not durable in contact with the 
soil, is straight-grained, and the best material for oars, 
etc. Used for agricultural implements, tool handles, 
automobile (rim boards), vehicle bodies and parts, 
baseball bats, interior finish, cabinet work, etc., etc. 
Basin of the Ohio, but found from Maine to Min- 
nesota and Texas. 

3. Red Ash (Fraxinus pubescens var. Pennsylvanica) . 

Medium- sized tree, a timber very similar to, but 
smaller than Fraxinus Americana. Heartwood light 
brown, sapwood lighter color. Wood heavy, hard, 
strong, and coarse-grained. Ranges from New 
Brunswick to Florida, and westward to Dakota, 
Nebraska, and Kansas. 

4. Black Ash {Fraxinus nigra var. samhucifolia) (Hoop 

Ash, Ground Ash) . Medium-sized tree, very common, 
is more widely distributed than the Fraxinus Ameri- 
cana; the wood is not so hard, but is well suited for 
hoops and basketwork. Heartwood dark brown, 
sapwood light brown or white. Wood heavy, rather 
soft, tough and coarse-grained. Used for barrel 
hoops, basketwork, cabinetwork and interior of 
houses. Maine to Minnesota and southward to 

5. Blue Ash {Fraxinus quadrangulata) . Small to medium- 

sized tree. Heartwood yellow, streaked with brown, 
sapwood a lighter color. Wood heavy, hard, and 
coarse-grained. Not common. Indiana and Illinois; 
occurs from Michigan to Minnesota and southward 
to Alabama. 

6. Green Ash {Fraxinus viridis). Small-sized tree. Oc- 

curs from New York to the Rocky Mountains, and 
southward to Florida and Arizona. 

7. Oregon Ash {Fraxinus Oregana). Small to medium- 

sized tree. Occurs from western Washington to 


8. Carolina Ash {Fraxinus Caroliniana). Medium-sized 

tree. Occurs in the Carohnas and the coast regions 

ASPEN (See Poplar) 


9. Basswood (Tilia Americana) (Linden, Lime Tree, 

American Linden, Lin, Bee Tree) . Medium- to large- 
sized tree. Wood light, soft, stiff, but not strong, 
of fine texture, straight and close-grained, and white 
to light brown color, but not durable in contact with 
the soil. The wood shrinks considerably in drying, 
works well and stands well in interior work. It is 
used for cooperage, in carpentry, in the manufacture 
of furniture and woodenware (both turned and carved), 
for toys, also for panelling of car and carriage bodies, 
for agricultural implements, automobiles, sides and 
backs of drawers, cigar boxes, excelsior, refrigerators, 
trunks, and paper pulp. It is also largely cut for 
veneer and used as "three-ply" for boxes and chair 
seats. It is used for sounding boards in pianos and 
organs. If well seasoned and painted it stands fairly 
well for outside work. Common in all northern 
broad-leaved forests. Found throughout the eastern 
United States, but reaches its greatest size in the 
Valley of the Ohio, becoming often 130 feet in height, 
but its usual height is about 70 feet. 

10. White Basswood {Tilia heterophylla) (Whitewood). 
A small-sized tree. Wood in its quality and uses 
similar to the preceding, only it is lighter in color. 
Most abundant in the Alleghany region. 

11. White Basswood (Tilia puhescens) (Downy Linden, 
Small-leaved Basswood). Small-sized tree. Wood 
in its quality and uses similar to Tilia Americana. 
This is a Southern species which makes it way as far 
north as Long Island. Is found at its best in South 



12. Beech (Fagus ferruginea) (Red Beech, White Beech). 
Medium-sized tree, common, sometimes forming 
forests of pure growth. Wood heavy, hard, stiff, 
strong, of rather coarse texture, white to Hght brown 
color, not durable in contact with the soil, and sub- 
ject to the inroads of boring insects. Rather close- 
grained, conspicuous medullary rays, and when 
quarter-sawn and well smoothed is very beautiful. 
The wood shrinks and checks considerably in drying, 
works well and stands well, and takes a fine polish. 
Beech is comparatively free from objectionable taste, 
and finds a place in the manufacture of commodities 
which come in contact with foodstuffs, such as lard 
tubs, butter boxes and pails, and the beaters of ice 
cream freezers; for the latter the persistent hardness 
of the wood when subjected to attrition and abrasion 
while wet gives it peculiar fitness. It is an excellent 
material for churns. Sugar hogsheads are made of 
beech, partly because it is a tasteless wood and partly 
because it has great strength. A large class of wooden- 
ware, including veneer plates, dishes, boxes, paddles, 
scoops, spoons, and beaters, which belong to the 
kitchen and pantry, are made of this species of wood. 
Beech picnic plates are made by the million, a single 
machine turning out 75,000 a day. The wood has 
a long list of miscellaneous uses and enters into 
a great variety of commodities. In every region 
where it grows in commercial quantities it is made 
into boxes, baskets, and crating. Beech baskets are 
chiefly employed in shipping fruit, berries, and vege- 
tables. In Maine thin veneer of beech is made 
specially for the Sicily orange and lemon trade. This 
is shipped in bulk and the boxes are made abroad. 
Beech is also an important handle wood, although 
not in the same class with hickory. It is not selected 
because of toughness and resiliency, as hickory is, 
and generally goes into plane, handsaw, pail, chisel, 


and flatiron handles. Recent statistics show that 
in the production of slack cooperage staves, only- 
two woods, red gum and pine, stood above beech in 
quantity, while for heading, pine alone exceeded it. 
It is also used in turnery, for shoe lasts, butcher 
blocks, ladder rounds, etc. Abroad it is very ex- 
tensively used by the carpenter, millwright, and wagon 
maker, in turnery and wood carving. Most abundant 
in the Ohio and Mississippi basin, but found from 
Maine to Wisconsin and southward to Florida. 


13. Cherry Birch (Betula lento) (Black Birch, Sweet Birch, 
Mahogany Birch, Wintergreen Birch). Medium- 
sized tree, very common. Wood of beautiful reddish 
or yellowish brown, and much of it nicely figured, 
of compact structure, is straight in grain, heavy, 
hard, strong, takes a fine polish, and considerably used 
as imitation of mahogany. The wood shrinks con- 
siderably in drying, works well and stands well, but 
is not durable in contact with the soil. The medul- 
lary rays in birch are very fine and close and not 
easily seen. The sweet birch is very handsome, with 
satiny luster, equalling cherry, and is too costly a 
wood to be profitably used for ordinary purposes, 
but there are both high and low grades of birch, the 
latter consisting chiefly of sapwood and pieces too 
knotty for first class commodities. This cheap ma- 
terial swells the supply of box lumber, and a little of 
it is found wherever birch passes through sawmills. 
The frequent objections against sweet birch as box 
lumber and crating material are that it is hard to 
nail and is inclined to split. It is also used for veneer 
picnic plates and butter dishes, although it is not 
as popular for this class of commodity as are yellow 
and paper birch, maple and beech. The best grades 
are largely used for furniture and cabinet work, and 
also for interior finish. Maine to Michigan and to 


14. White Birch (Betula populifolia) (Gray Birch, Old 
Field Birch, Aspen-leaved Birch). Small to medium- 
sized tree, least common of all the birches. Short- 
hved, twenty to thirty feet high, grows very rapidly. 
Heartwood hght brown, sapwood lighter color. Wood 
hght, soft, close-grained, not strong, checks badly 
in drying, decays quickly, not durable in contact 
with the soil, takes a good polish. Used for spools, 
shoepegs, wood pulp, and barrel hoops. Fuel value 
not high, but burns with bright flame. Ranges from 
Nova Scotia and lower St. Lawrence River, south- 
ward, mostly in the coast region to Delaware, and 
westward through northern New England and New 
York to southern shore of Lake Ontario. 

15. Yellow Eirch (Betula lutea) (Gray Birch, Silver Birch). 
Medium- to large-sized tree, very common. Heart- 
wood light reddish brown, sapwood nearly white, 
close-grained, compact structure, with a satiny luster. 
Wood heavy, very strong, hard, tough, susceptible 
of high polish, not durable when exposed. Is similar 
to Betula lenta, and finds a place in practically all 
kinds of woodenware. A large percentage of broom 
handles on the market are made of this species of 
wood, though nearly every other birch contributes 
something. It is used for veneer plates and dishes 
made for pies, butter, lard, and many other com- 
modities. Tubs and pails are sometimes made of 
yellow birch provided weight is not objectionable. 
The wood is twice as heavy as some of the pines and 
cedars. Many small handles for such articles as 
flatirons, gimlets, augers, screw drivers, chisels, var- 
nish and paint brushes, butcher and carving knives, 
etc. It is also widely used for shipping boxes, baskets, 
and crates, and it is one of the stiffest, strongest 
woods procurable, but on account of its excessive 
weight it is sometimes discriminated against. It 
is excellent for veneer boxes, and that is probably 
one of the most important places it fills. Citrus 
fruit from northern Africa and the islands and coun- 
tries of the Mediterranean is often shipped to market 


in boxes made of yellow birch from veneer cut in 
New England. The bett-^r grades are also used for 
furniture and cabinet work, and the "burls" found 
on this species are highly valued for making fancy 
articles, gavels, etc. It is extensively used for turnery, 
buttons, spools, bobbins, wheel hubs, etc. Maine 
to Minnesota and southward to Tennessee. 

16. Red Birch (Betula rubra var. nigra) (River Birch). 
Small to medium-sized tree, very common. Lighter 
and less valuable than the preceding. Heartwood 
hght brown, sapwood pale. Wood hght, fairly strong 
and close-grained. Red birch is best developed in 
the middle South, and usually grows near the banks 
of rivers. Its bark hangs in tatters, even worse than 
that of paper birch, but it is darker. In Tennessee 
the slack coopers have found that red birch makes 
excellent barrel heads and it is sometimes employed 
in preference to other woods. In eastern Maryland 
the manufacturers of peach baskets draw their sup- 
phes from this wood, and substitute it for white elm 
in making the hoops or bands which stiffen the top 
of the basket, and provide a fastening for the veneer 
which forms the sides. Red birch bends in a very 
satisfactory manner, which is an important pomt. 
This wood enters pretty generally into the manu- 
facture of woodenware within its range, but statistics 
do not mention it by name. It is also used in the 
manufacture of veneer picnic plates, pie plates, butter 
dishes, washboards, small handles, kitchen and pantry 
utensils, and ironing boards. New England to Texas 
and Missouri. 

17. Canoe Birch {Betula paprifera) (White Birch, Paper 
Birch). Small to medium-sized tree, sometimes form- 
ing forests, very common. Heartwood hght brown 
tinged with red, sapwood hghter color. Wood of 
good quahty, but hght, fairly hard and strong, tough, 
close-grained. Sap flows freely in sprmg and by 
boihng can be made into syrup. Not as valuable as 
any of the preceding. Canoe birch is a northern 


tree, easily identified by its white trunk and its ragged 
bark. Large numbers of small wooden boxes are 
made by boring out blocks of this wood, shaping 
them in lathes, and fitting lids on them. Canoe 
birch is one of the best woods for this class of com- 
modities, because it can be worked very thin, does 
not split readily, and is of pleasing color. Such boxes, 
or two-piece diminutive kegs, are used as containers 
for articles shipped and sold in small bulk, such as 
tacks, small nails, and brads. Such containers are 
generally cylindrical and of considerably greater depth 
than diameter. Many others of nearly similar form 
are made to contain ink bottles, bottles of perfumery, 
drugs, liquids, salves, lotions, and powders of many 
kinds. Many boxes of this pattern are used by 
manufacturers of pencils and crayons for packing 
and shipping their wares. Such boxes are made in 
numerous numbers by automatic machinery. A 
single machine of the most improved pattern will 
turn out 1,400 boxes an hour. After the boring and 
turning are done, they are smoothed by placing them 
into a tumbling barrel with soapstone. It is also 
used for one-piece shallow trays or boxes, without 
lids, and used as card receivers, pin receptacles, 
butter boxes, fruit platters, and contribution plates 
in churches. It is also the principal wood used for 
spools, bobbins, bowls, shoe lasts, pegs, and turnery, 
and is also much used in the furniture trade. All 
along the northern boundary of the United States 
and northward, from the Atlantic to the Pacific. 

BLACK WALNUT (See Walnut) 


18. Blue Beech (Carpinus Caroliniana) (Hornbeam, Water 
Beech, Ironwood). Small-sized tree. Heartwood 
light brown, sapwood nearly white. Wood very hard, 
heavy, strong, very stiff, of rather fine texture, not 
durable in contact with the soil, shrinks and checks 
considerably in drying, but works well and stands 


well, and takes a fine polish. Used chiefly in turnery, 
for tool handles, etc. Abroad much used by mill- 
and wheelwrights. A small tree, largest in the South- 
west, but found in nearly all parts of the eastern 
United States. 

BOIS D'ARC (See Osage Orange) 


Wood light, soft, not strong, often quite tough, of fine, 
uniform texture and creamy white color. It shrinks con- 
siderably in drying, but works well and stands well. Used 
for woodenware, artificial limbs, paper pulp, and locally 
also for building construction. 

19. Ohio Buckeye {Msculus glabra) (Horse Chestnut, 
Fetid Buckeye). Small-sized tree, scattered, never 
forming forests. Heartwood white, sapwood pale 
brown. Wood light, soft, not strong, often quite 
tough and close-grained. Alleghanies, Pennsylvania 
to Oklahoma. 

20. Sweet Buckeye {Msculus octandra var. flava) (Horse 
Chestnut). Small-sized tree, scattered, never form- 
ing forests. Wood in its quality and uses similar to 
the preceding. Alleghanies, Pennsylvania to Texas. 


21. Buckthorne {Rhanmus Caroliniana) (Indian Cherry). 
Small-sized tree. Heartwood light brown, sapwood 
almost white. Wood hght, hard, close-grained. Does 
not enter the markets to any great extent. Found 
along the borders of streams in rich bottom lands. 
Its northern limits is Long Island, where it is only 
a shrub; it becomes a tree only in southern Arkansas 
and adjoining regions. 


22. Butternut {Juglans cinerea) (White Walnut, White 
Mahogany, Walnut). Medium-sized tree, scattered, 


never forming forests. Wood very similar to black 
walnut, but light, quite soft, and not strong. Heart- 
wood light gray-brown, darkening with exposure; 
sapwood nearly white, coarse-grained, compact struc- 
ture, easily worked, and susceptible to high polish. 
Has similar grain to black walnut and when stained 
is a very good imitation. Is much used for inside 
work, and very durable. Used chiefly for finishing 
lumber, cabinet work, boat finish and fixtures, and 
for furniture. Butternut furniture is often sold as 
Circassian walnut. Largest and most common in the 
Ohio basin. Maine to Minnesota and southward 
to Georgia and Alabama. 


The catalpa is a tree which was planted about 25 years 
ago as a commercial speculation in Iowa, Kansas, and 
Nebraska. Its native habitat was along the rivers Ohio 
and lower Wabash, and a century ago it gained a repu- 
tation for rapid growth and durability, but did not grow 
in large quantities. As a railway tie, experiments have 
left no doubt as to its resistence to decay; it stands ab- 
rasion as well as the white oak {Quercus alba), and is 
superior to it in longevity. Catalpa is a tree singularly 
free from destructive diseases. Wood cut from the living 
tree is one of the most durable timbers known. In spite 
of its light porous structure it resists the weathering in- 
fluences and the attacks of wood-destroying fungi to a 
remarkable degree. No fungus has yet been found which 
will grow in the dead timber, and for fence posts this wood 
has no equal, lasting longer than almost any other species 
of timber. The wood is rather soft and coarse in texture, 
the tree is of slow growth, and the brown colored heartwood, 
even of very young trees, forms nearly three-quarters of 
their volume. There is only about one-quarter inch of 
sapwood in a 9-inch tree. 

23. Catalpa {Catalpa speciosa var. bignonioides) (Indian 
Bean). Medium-sized tree. Heartwood hght brown, 
sapwood nearly white. Wood light, soft, not strong, 


brittle, very durable in contact with the soil, of coarse 
texture. Used chiefly for railway ties, telegraph poles, 
and fence posts, but well suited for a great variety of 
uses. Lower basin of the Ohio River, locally com- 
mon. Extensively planted, and therefore promising 
to become of some importance. 


24. Cherry {Prunus serotina) (Wild Cherry, Black Cherry, 
Rum Cherry). Wood heavy, hard, strong, of fine 
texture. Sapwood yellowish white, heartwood reddish 
to brown. The wood shrinks considerably in drying, 
works well and stands well, has a fine satin-like luster, 
and takes a fine polish which somewhat resembles 
mahogany, and is much esteemed for its beauty. 
Cherry is chiefly used as a decorative interior finish- 
ing lumber, for buildings, cars and boats, also for 
furniture and in turnery, for musical instruments, 
walking sticks, last blocks, and woodenware. It is 
becoming too costly for many purposes for which it 
is naturally well suited. The lumber-furnishing 
cherry of the United States, the wild black cherry, 
is a small to medium-sized tree, scattered through 
many of the broad-leaved trees of the western slope 
of the AUeghanies, but found from Michigan to 
Florida, and west to Texas. Other species of this 
genus, as well as the hawthornes {Prunus cratoegus) 
and wild apple (Pyrus), are not commonly offered in 
the markets. Their wood is of the same character 
as cherry, often finer, but in smaller dimensions. 

25. Red Cherry (Prunus Pennsylvanica) (Wild Red Cherry, 
Bird Cherry). Small-sized tree. Heartwood light 
brown, sapwood pale yellow. Wood light, soft, and 
close-grained. Uses similiar to the preceding, com- 
mon throughout the Northern States, reaching its 
greatest size on the mountains of Tennessee. 



The chestnut is a long-hved tree, attaining an age of 
from 400 to 600 years, but trees over 100 years are usually 
hollow. It grows quickly, and sprouts from a chestnut 
stump (Coppice Chestnut) often attain a height of 8 feet 
in the first year. It has a fairly cylindrical stem, and 
often grows to a height of 100 feet and over. Coppice 
chestnut, that is, chestnut grown on an old stump, furnishes 
better timber for working than chestnut grown from the 
nut, it is heavier, less spongy, straighter in grain, easier 
to split, and stands exposure longer. 

26. Chestnut {Castanea vulgaris var. Americana). Me- 
dium- to large-sized tree, never forming forests. Wood 
is light, moderately hard, stiff, elastic, not strong, 
but very durable when in contact with the soil, of 
coarse texture. Sapwood light, heartwood darker 
brown, and is readily distinguishable from the sap- 
wood, which very early turns into heartwood. It 
shrinks and checks considerably in drying, works 
easily, stands well. The annual rings are very dis- 
tinct, medullary rays very minute and not visible to 
the naked eye. Used in cooperage, for cabinetwork, 
agricultural implements, railway ties, telegraph poles, 
fence posts, sills, boxes, crates, coffins, furniture, 
fixtures, foundation for veneer, and locally in heavy 
construction. Very common in the Alleghanies. Oc- 
curs from Maine to Michigan and southward to 

27. Chestnut {Castanea dentata var. vesca). Medium- 
sized tree, never forming forests, not common. 
Heart-wood brown color, sapwood lighter shade, 
coarse-grained. Wood and uses similar to the preced- 
ing. Occurs scattered along the St. Lawrence River, 
and even there is met with only in small quantities. 

28. Chinquapin {Castanea pumila). Medium- to small- 
sized tree, with wood slightly heavier, but otherwise 
similiar to the preceding. Most common in Arkansas, 
but with nearly the same range as Castanea vulgaris. 


29. Chinquapin {Castanea chrysophylla) . A medium-sized 
tree of the western ranges of Cahfornia and Oregon. 


30. Coffee Tree (Gymnocladus dioicus) (Coffee Nut, 
Stump Tree). A medium- to large-sized tree, not 
common. Wood heavy, hard, strong, very stiff, of 
coarse texture, and durable. Sapwood yellow, heart- 
wood reddish brown, shrinks and checks considerably 
in drying, works well and stands well, and takes a 
fine polish. It is used to a limited extent in cabinet- 
work and interior finish. Pennsylvania to Min- 
nesota and Arkansas. 

COTTONWOOD (See Poplar) 


31. Crab Apple {Pyrus coronaria) (Wild Apple, Fragrant 
Crab). Small-sized tree. Heartwood reddish brown, 
sapwood yellow. Wood heavy, hard, not strong, 
close-grained. Used principally for tool handles and 
small domestic articles. Most abundant in the middle 
and western states, reaches its greatest size in the 
valleys of the lower Ohio basin. 

CUCUMBER TREE (See Magnolia) 


32. Dogwood (Cornus florida) (American Box). Small to 
medium-sized tree. Attains a height of about 30 
feet and about 12 inches in diameter. The heart- 
wood is a red or pinkish color, the sapwood, which is 
considerable, is a creamy white. The wood has a 
dull surface and very fine grain. It is valuable for 
turnery, tool handles, and mallets, and being so free 
from silex, watchmakers use small splinters of it for 
cleaning out the pivot holes of watches, and opticians 
for removing dust from deep-seated lenses. It is 


also used for butchers' skewers, and shuttle blocks 
and wheel stock, and is suitable for turnery and inlaid 
work. Occurs scattered in all the broad-leaved forests 
of our country; very common. 


Wood heavy, hard, strong, elastic, very tough, moder- 
ately durable in contact with the soil, commonly cross- 
grained, difficult to split and shape, warps and checks 
considerably in drying, but stands well if properly seasoned. 
The broad sapwood whitish, heartwood light brown, both 
with shades of gray and red. On split surfaces rough, 
texture coarse to fine, capable of high polish. Elm for 
years has been the principal wood used in slack cooperage 
jfor barrel staves, also in the construction of cars, wagons, 
etc., in boat building, agricultural implements and ma- 
chinery, in saddlery and harness work, and particu- 
larly in the manufacture of all kinds of furniture, where 
the beautiful figures, especially those of the tangential or 
bastard section, are just beginning to be appreciated. 
The elms are medium- to large-sized trees, of fairly rapid 
growth, with stout trunks; they form no forests of pure 
growth, but are found scattered in all the broad-leaved 
woods of our country, sometimes forming a considerable 
portion of the arborescent growth. 

33. White Elm (Ulmus Americana) (American Elm, Water 
Elm). Medium- to large-sized tree. Wood in its 
quality and uses as stated above. Common. Maine 
to Minnesota, southward to Florida and Texas. 

34. Rock Elm. (Ulmus racemosa) (Cork Elm, Hickory Elm, 
White Elm, Cliff Elm). Medium- to large-sized tree 
of rapid growth. Heartwood light brown, often 
tinged with red, sapwood yellowish or greenish white, 
compact structure, fibres interlaced. Wood heavy, 
hard, very tough, strong, elastic, difficult to split, 
takes a fine polish. Used for agricultural imple- 
ments, automobiles, crating, boxes, cooperage, tool 
handles, wheel stock, bridge timbers, sills, interior 


finish, and maul heads. Fairly free from knots and 
has only a small quantity of sapwood. Michigan, 
Ohio, from Vermont to Iowa, and southward to 

35. Red Elm {Ulmus fulva var. puhescens) (Slippery Elm, 
Moose Elm). The red or shppery elm is not as large 
a tree as the white elm ( Ulmus Americana), though 
it occasionally attains a height of 135 feet and a di- 
ameter of 4 feet. It grows tall and straight, and 
thrives in river valleys. The wood is heavy, hard, 
strong, tough, elastic, commonly cross-grained, mod- 
erately durable in contact with the soil, spHts easily 
when green, works fairly well, and stands well if 
properly handled. Careful seasoning and handhng 
are essential for the best results. Trees can be 
utihzed for posts when very small. When green the 
wood rots very quickly in contact with the soil. 
Poles for posts should be cut in summer and peeled 
and dried before setting. The wood becomes very 
tough and phable when steamed, and is of value for 
sleigh runners and for ribs of canoes and skiffs. To- 
gether with white elm ( Ulmus Americana) it is ex- 
tensively used for barrel staves in slack cooperage 
and also for furniture. The thick, viscous inner 
bark, which gives the tree its descriptive name, is 
quite palatable, slightly nutritious, and has a medi- 
cinal value. Found chiefly along water courses. 
New York to Minnesota, and southward to Florida 
and Texas. 

36. Cedar Elm {Ulmus crassifolia) . Medium- to small- 
sized tree, locally quite common. Arkansas and 

37. Winged Elm {Ulmus alata) (Wahoo). Small-sized 
tree, locally quite common. Heartwood light brown, 
sapwood yellowish white. Wood heavy, hard, tough, 
strong, and close-grained. Arkansas, Missouri, and 
eastern Virginia. 




This general term applies to three important species 
of gum in the South, the principal one usually being dis- 
tinguished as "red" or "sweet" gum (see Fig. 10). 
The next in importance being the "tupelo" or "bay pop- 
lar," and the least of the trio is designated as "black" or 
"sour" gum (see Fig. 11). Up to the year 1900 little 
was known of gum as a wood for cooperage purposes, but 

Fig. 10. A Large Red Gum. 


by the continued advance in price of the woods used, a 
few of the most progressive manufacturers, looking into 
the future, saw that the supply of the various woods in 
use was limited, that new woods would have to be sought, 
and gum was looked upon as a possible substitute, owing 
to its cheapness and abundant supply. No doubt in the 
future this wood will be used to a considerable extent in 
the manufacture of both "tight" and "slack" cooperage. 

Fig. 11. A Tupelo Gum Slough. 


In the manufacture of the gum, unless the knives and 
saws are kept very sharp, the wood has a tendency to 
break out, the corners sphtting off; and also, much dif- 
ficulty has been experienced in seasoning and kiln-drying. 
In the past, gum, having no marketable value, has been 
left standing after logging operations, or, where the land 
has been cleared for farming, the trees have been "girdled" 
and allowed to rot, and then felled and burned as trash. 
Now, however, that there is a market for this species of 
timber, it will be profitable to cut the gum with the other 
hardwoods, and this species of wood will come in for a 
greater share of attention than ever before. 

38. Red Gum. {Liquidamher styraciflua) (Sweet Gum, 
Hazel Pine, Satin Walnut, Liquidamber, Bilsted). 
The wood is about as stiff and as strong as chestnut, 
rather heavy, it splits easily and is quite brash, com- 
naonly cross-grained, of fine texture, and has a large 
proportion of whitish sapwood, which decays rapidly 
when exposed to the weather; but the reddish brown 
heartwood is quite durable, even in the ground. The 
external appearance of the wood is of fine grain and 
' smooth, close texture, but when broken the lines of 
fracture do not run with apparent direction of the 
growth; possibly it is this unevenness of grain which 
renders the wood so difficult to dry without twisting 
and warping. It has little resiliency; can be easily 
bent when steamed, and when properly dried will 
hold its shape. The annual rings are not distinctly 
marked, medullary rays fine and numerous. The 
green wood contains much water, and consequently is 
heavy and difficult to float, but when dry it is as light 
as basswood. The great amount of water in the 
green wood, particularly in the sap, makes it difficult 
to season by ordinary methods without warping and 
twisting. It does not check badly, is tasteless and 
odorless, and when once seasoned, swells and shrinks 
but little unless exposed to the weather. Used for 
boat finish, veneers, cabinet work, furniture, fixtures, 
interior decoration, shingles, paving blocks, wooden- 


ware, cooperage, machinery frames, refrigerators, and 
trunk slats. 

Range of Red Gum 

Red gum is distributed from Fairfield County, Conn., 
to southeastern Missouri, through Arkansas and Okla- 
homa to the valley of the Trinity River in Texas, 
and eastward to the Atlantic coast. Its commer- 
cial range is restricted, however, to the moist lands of 
the lower Ohio and Mississippi basins and of the South- 
eastern coast. It is one of the commonest timber trees 
in the hardwood bottoms and drier swamps of the South. 
It grows in mixture with ash, cottonwood and oak (see 
Fig. 12). It is also found to a considerable extent on 
the lower ridges and slopes of the southern Appalachians, 
but there it does not reach merchantable value and is of 
little importance. Considerable difference is found be- 
tween the growth in the upper Mississippi bottoms and 
that along the rivers on the Atlantic coast and on the 
Gulf. In the latter regions the bottoms are lower, and 
consequently more subject to floods and to continued 
overflows (see Fig. 11). The alluvial deposit is also greater, 
and the trees grow considerably faster. Trees of the same 
diameter show a larger percentage of sapwood there than 
in the upper portions of the Mississippi Valley. The 
Mississippi Valley hardwood trees are for the most part 
considerably older, and reach larger dimensions than the 
timber along the coast. 

Form of the Red Gum 

In the best situations red gum reaches a height of 150 
feet, and a diameter of 5 feet. These dimensions, how- 
ever, are unusual. The stem is straight and cylindrical, 
with dark, deeply-furrowed bark, and branches often 
winged with corky ridges. In youth, while growing vigor- 
ously under normal conditions, it assumes a long, regular, 
conical crown, much resembling the form of a conifer 
(see Fig. 12). After the tree has attained its height 
growth, however, the crown becomes rounded, spreading 
and rather ovate in shape. When growing in the forest 


the tree prunes itself readily at an early period, and forms 
a good length of clear stem, but it branches strongly after 
making most of its height growth. The mature tree is 
usually forked, and the place where the forking commences 
determines the number of logs in the tree or its merchant- 
able length, by preventing cutting to a small diameter in 
the top. On large trees the stem is often not less than 
eighteen inches in diameter where the branching begins. 
The over-mature tree is usually broken and dry topped, 
with a very spreading crown, in consequence of new 
branches being sent out. 

Tolerance of Red Gum 

Throughout its entire life red gum is intolerant in shade, 
there are practically no red seedlings under the dense 
forest cover of the bottom land, and while a good many 
may come up under the pine forest on the drier uplands, 
they seldom develop into large trees. As a rule seedlings 
appear only in clearings or in open spots in the forest. It 
is seldom that an over-topped tree is found, for the gum 
dies quickly if suppressed, and is consequently nearly 
always a dominant or intermediate tree. In a hardwood 
bottom forest the timber trees are all of nearly the same 
age over considerable areas, and there is little young 
growth to be found in the older stands. The reason for 
this is the intolerance of most of the swamp species. A 
scale of intolerance containing the important species, and 
beginning with the most light-demanding, would run as 
follows: Cottonwood, sycamore, red gum, white elm, 
white ash, and red maple. 

Demands upon Soil and Moisture 

While the red gum grows in various situations, it pre- 
fers the deep, rich soil of the hardwood bottoms, and there 
reaches its best development (see Fig. 10). It re- 
quires considerable soil moisture, though it does not grow 
in the wetter swamps, and does not thrive on dry pine land. 
Seedlings, however, are often found in large numbers on 
the edges of the uplands and even on the sandy pine land, 
but they seldom live beyond the pole stage. When they 


do, they form small, scrubby trees that are of Httle value. 
Where the soil is dry the tree has a long tap root. In the 
swamps, where the roots can obtain water easily, the de- 
velopment of the tap root is poor, and it is only moderate 
on the glade bottom lands, where there is considerable 
moisture throughout the year, but no standing water in 
the summer months. 

Reproduction of Red Gum 

Red gum reproduces both by seed and by sprouts 
(see Fig. 12). It produces seed fairly abundantly every 
year, but about once in three years there is an extremely 

Fig. 12. Second Growth Red Gum, Ash, Cottonwood, and Sycamore. 

heavy production. The tree begins to bear seed when 
twenty-five to thirty years old, and seeds vigorously up 
to an age of one hundred and fifty years, when its pro- 
ductive power begins to diminish. A great part of the 
seed, however, is abortive. Red gum is not fastidious in 
regard to its germinating bed; it comes up readily on sod 



in old fields and meadows, on decomposing homus in the 
forest, or on bare clay-loam or loamy sand soil. It re- 
quires a considerable degree of light, however, and prefers 
a moist seed bed. The natural distribution of the seed 
takes place for several hundred feet from the seed trees, 
the dissemination depending almost entirely on the wind. 
A great part of the seed falls on the hardwood bottom when 
the land is flooded, and is either washed away or, if already 

LpB^P^S^BBPP"'™''"'^" -»*—*■*-> -^ 

Fig. 13. A Cypress Slough in the Dry Season. 


in the ground and germinating, is destroyed by the long- 
continued overflow. After germinating, the red gum 
seedhng demands, above everything else, abundant hght 
for its survival and development. It is for this reason 
that there is very little growth of red gum, either m the 
unculled forest or on culled land, where, as is usually the 
case, a dense undergrowth of cane, briers, and rattan is 
present. Under the dense underbrush of cane and briers 
throughout much of the virgin forest, reproduction of any 
of the merchantable species is of course impossible. And 
even where the land has been logged over, the forest is 
seldom open enough to allow reproduction of cottonwood 
and red gum. Where, however, seed trees are contiguous 
to pastures or cleared land, scattered seedhngs are found 
springing up in the open, and where openings occur m the 
forest, there are often large numbers of red gum seedhngs, 
the reproduction generally occuring in groups. But over 
the greater part of the Southern hardwood bottoni land 
forest reproduction is very poor. The growth of red gum 
during the early part of its life, and up to the time it 
reaches a diameter of eight inches breast-high, is extremely 
rapid, and, like most of the intolerant species, it attains 
its height growth at an early period. Gum sprouts readily 
from the stump, and the sprouts surpass the seedhngs m 
rate of height growth for the first few years, but they sel- 
dom form large timber trees. Those over fifty years of 
age seldom sprout. For this reason sprout reproduction 
is of Uttle importance in the forest. The principal re- 
quirements of red gum, then, are a moist, fairly rich soil 
and good exposure to hght. Without these it will not 
reach its best development. 

Second-Growth Red Gum 

Second-growth red gum occurs to any considerable ex- 
tent only on land which has been thoroughly cleared. 
Throughout the South there is a great deal of land which 
was in cultivation before the Civil War, but which during 
the subsequent period of industrial depression was aban- 
doned and allowed to revert to forest. These old fields 
are now mostly covered with second-growth forest, ot 


which red gum forms an important part (see Fig. 12). 
Frequently over fifty per cent of the stand consists of this 
species, but more often, and especially on the Atlantic 
coast, the greater part is of cottonwood or ash. These 
stands are very dense, and the growth is extremely rapid. 
Small stands of young growth are also often found along 
the edges of cultivated fields. In the Mississippi Valley 
the abandoned fields on which young stands have sprung 
up are for the most part being rapidly cleared again. The 
second growth here is considered of little value in com- 
parison with the value of the land for agricultural purposes. 
In many cases, however, the farm value of the land is not 
at present sufficient to make it profitable to clear it, unless 
the timber cut will at least pay for the operation. There 
is considerable land upon which the second growth will 
become valuable timber within a few years. Such land 
should not be cleared until it is possible to utilize the 

39. Tupelo Gum {Nyssa aquatica) (Bay Poplar, Swamp 
Poplar, Cotton Gum, Hazel Pine, Circassian Walnut, 
Pepperidge, Nyssa). The close similarity which ex- 
ists between red and tupelo gum, together with the 
fact that tupelo is often cut along with red gum, and 
marketed with the sapwood of the latter, makes it 
not out of place to give consideration to this timber. 
The wood has a fine, uniform texture, is moderately 
hard and strong, is stiff, not elastic, very tough and 
hard to split, but easy to work with tools. Tupelo 
takes glue, paint, or varnish well, and absorbs very 
little of the material. In this respect it is equal to 
yellow poplar and superior to cottonwood. The 
wood is not durable in contact with ground, and re- 
quires much care in seasoning. The distinction be- 
tween the heartwood and sapwood of this species is 
marked. The former varies in color from a dull gray 
to a dull brown; the latter is whitish or light yellow 
like that of poplar. The wood is of medium weight, 
about thirty-two pounds per cubic foot when dry, or 
nearly that of red gum and loblolly pine. After 

seasoning it is difficult to d-ti^sui.h the better g^^^^^^^ 
of saowood from poplar. Owing to the prejuoice 
aL nst tupelo gum, it was until recently marketed 
under sucTnamL as bay poplar, swamp poplar, nyssa 
cotton gum, Circassian walnut, and hazel pme Smce 
it hrbecoike evident that the properties of the wood 
fit iff or many uses, the demand for tupelo has largely 
fncreased and it is now taking rank with other stand- 
ard wool under its rightful name. Heretofore the 
oualiTv and usefulness of this wood were greatly 
Se estimated, and the difficulty of h-^Uing i* wa 
mamified. Poor success in seasonmg and kiln-dry 
SgTas laid to defects o£ the wood itself, jhen as a 

matTer of fact, the failures \«- j-S^'y ^e mss ng 
absence of proper methods m handlmg. The passing 
of tWs prejudice against tupelo is due to a better 
undtZdLg of th'e characteristics and uses oMh 
wood. Handled in the way m which its Particular 
Tharacter demands, tupelo is a wood of much value. 

Uses of Tupelo Gum 

Tunelo gum is now used in slack cooperage principally 
for heatnf It is used extensively for house floormg and 
nside fiSng, such as mouldings, door jambs, and casings 
rSat dtll now shipped to European «-« J^'^f;^ 
■I % \\Mv valued for different classes of manutacture. 
Cch' f 'Ife W is used in the manufacture of b^-. -- 

^nlnSe^a^Sra^dr tl^XrXwor P^P , 
:S.r:T rgan sounding boaKl^-^^ofi- mantelwork. 
conduits and novelties. It is also usea 
trade for backing, drawers, and panels. 

Range of Tupelo Gum 

Tupelo occurs throughout the coastal region of the At- 

r^^ ftr cKaTef tTtiT; vX "f r Xe!r :; 

Tritt^St^^^ and southe- Missouri to 
western Kentucky and Tennessee, and to the valley 


the lower Wabash River. Tupelo is being extensively 
milled at present only in the region adjacent to Mobile, 
Ala., and in southern and central Louisiana, where it 
occurs in large merchantable quantities, attaining its 
best development in the former locahty. The country 
in this locahty is very swampy (see Fig. 11), and within 
a radius of one hundred miles tupelo gum is one of the 
principal timber trees. It grows only in the swamps and 
wetter situations (see Fig. 11), often in mixture with 
cypress, and in the rainy season it stands in from two to 
twenty feet of water. 

40. Black Gum {Nyssa sylvatica) (Sour Gum). Black 
gum is not cut to much extent, owing to its less abun- 
dant supply and poorer quality, but is used for repair 
work on wagons, for boxes, crates, wagon hubs, 
rollers, bowls, woodenware, and for cattle yokes and 
other purposes which require a strong, non-sphtting 
wood. Heartwood is light brown in color, often 
nearly white; sap wood hardly distinguishable, fine 
grain, fibres interwoven. Wood is heavy, not hard, 
difficult to work, strong, very tough, checks and 
warps considerably in drying, not durable. It is 
distributed from Maine to southern Ontario, through 
central Michigan to southeastern Missouri, south- 
ward to the valley of the Brazos River in Texas, and 
eastward to the Kissimmee River and Tampa Bay 
in Florida. It is found in the swamps and hardwood 
bottoms, but is more abundant and of better size on the 
slightly higher ridges and hummocks in these swamps, 
and on the mountain slopes in the southern Alleghany 
region. Though its range is greater than that of 
either red or tupelo gum, it nowhere forms an im- 
portant part of the forest. 


41. Hackberry {Celtis occidentalis) (Sugar Berry, Nettle 
Tree). The wood is handsome, heavy, hard, strong, 
quite tough, of moderately fine texture, and greenish 
or yellowish color, shrinks moderately, works well 


and stands well, and takes a good polish. Used to 
some extent in cooperage, and in the manufacture of 
cheap furniture. Medium- to large-sized tree, locally 
quite common, largest in the lower Mississippi Valley. 
Occurs in nearly all parts of the eastern United States. 


The hickories of commerce are exclusively North Ameri- 
can, and some of them are large and beautiful trees of 
60 to 70 feet or more in height. They are closely allied 
to the walnut, and the wood is very like walnut in grain 
and color, though of a somewhat darker brown. It is one 
of the finest of American hardwoods in point of strength; 
in toughness it is superior to ash, rather coarse in texture, 
smooth and of straight grain, very heavy and strong as 
well as elastic and tenacious, but decays rapidly, especially 
the sapwood when exposed to damp and moisture, and 
is very liable to attack from worms and boring insects. 
The cross-section of hickory is peculiar, the annual rings 
appear like fine lines instead of like the usual pores, and 
the medullary rays, which are also very fine but distinct, 
in crossing these form a peculiar web-like pattern which 
is one of the characteristic differences between hickory 
and ash. Hickory is rarely subjected to artificial treat- 
ment, but there is this curious fact in connection with the 
wood, that, contrary to most other woods, creosote is 
only with difficulty injected into the sap, although there 
is no difficulty in getting it into the heartwood. It dries 
slowly, shrinks and checks considerably in seasoning; is not 
durable in contact with the soil or if exposed. Hickory 
excels as wagon and carriage stock, for hoops in cooperage, 
and is extensively used in the manufacture of imple- 
ments and machinery, for tool handles, timber pins, 
harness work, dowel pins, golf clubs, and fishing rods. 
The hickories are tall trees with slender stems, never form- 
ing forests, occasionally small groves, but usually occur 
scattered among other broad-leaved trees in suitable locali- 
ties. The following species all contribute more or less 
to the hickory of the markets: 


42. Shagbark Hickory (Hicoria ovata) (Shellbark Hick- 
ory, Scalybark Hickory). A medium- to large-sized 
tree, quite common ; the favorite among the hickories. 
Heartwood light brown, sapwood ivory or cream- 
colored. Wood close-grained, compact structure, 
annual rings clearly marked. Very hard, heavy, 
strong, tough, and flexible, but not durable in con- 
tact with the soil or when exposed. Used for agri- 
cultural implements, wheel runners, tool handles, 
vehicle parts, baskets, dowel pins, harness work, golf 
clubs, fishing rods, etc. Best developed in the Ohio 
and Mississippi basins; from Lake Ontario to Texas, 
Minnesota to Florida. 

43. Mockernut Hickory {Hicoria alba) (Black Nut Hick- 
ory, Black Hickory, Bull Nut Hickory, Big Bud 
Hickory, White Heart Hickory) . A medium- to large- 
sized tree. Wood in its quality and uses similar to 
the preceding. Its range is the same as that of 
Hicoria ovata. Common, especially in the South. 

44. Pignut Hickory (Hicoria glabra) (Brown Hickory, 
Black Hickory, Switchbud Hickory). A medium- to 
large-sized tree. Heavier and stronger than any 
of the preceding. Heartwood light to dark brown, 
sapwood nearly white. Abundant, all eastern United 

45. Bitternut Hickory (Hicoria minima) (Swamp Hick- 
ory). A medium-sized tree, favoring wet localities. 
Heartwood light brown, sapwood lighter color. Wood 
in its quality and uses not so valuable as Hicoria 
ovata, but is used for the same purposes. Abundant, 
all eastern United States. 

46. Pecan (Hicoria pecan) (Illinois Nut). A large tree, 
very common in the fertile bottoms of the western 
streams. Indiana to Nebraska and southward to 
Louisiana and Texas. 


47. Holly (Hex opaca). Small to medium-sized tree. 
Wood of medium weight, hard, strong, tough, of 


exceedingly fine grain, closer in texture than most 
woods, of white color, sometimes almost as white as 
ivory; requires great care in its treatment to pre- 
serve the whiteness of the wood. It does not readily 
absorb foreign matter. Much used by turners and 
for all parts of musical instruments, for handles on 
whips and fancy articles, draught-boards, engraving ' 
blocks, cabinet work, etc. The wood is often dyed 
black and sold as ebony; works well and stands well. 
Most abundant in the lower Mississippi Valley and 
Gulf States, but occuring eastward to Massachusetts 
and north to Indiana. 

48. Holly {Ilex monticolo) (Mountain Holly). Small- 
sized tree. Wood in its quaUty and uses similar to 
the preceding, but is not very generally known. It 
is found in the Catskill Mountains and extends south- 
ward along the Alleghanies as far as Alabama. 



49. Ironwood (Ostrya Virginiana) (Hop Hornbeam, Lever 
Wood). Small-sized tree, common. Heartwood light 
brown tinged with red, sapwood nearly white. Wood 
heavy, tough, exceedingly close-grained, very strong 
and hard, durable in contact with the soil, and will 
take a fine polish. Used for small articles hke levers, 
handles of tools, mallets, etc. Ranges throughout 
the United States east of the Rocky Mountains. 


50. Lsiurel (Umbellularia Calif ornica) (Mjrtle). A West- 
ern tree, produces timber of hght brown color of great 
size and beauty, and is very valuable for cabinet and 
inside work, as it takes a fine polish. California and 
Oregon, coast range of the Sierra Nevada Mountains. 



51. Black Locust {Rohinia pseudacacia) (Locust, Yellow 
Locust, Acacia). Small to medium-sized tree. Wood 
very heavy, hard, strong, and tough, rivalhng some 
of the best oak in this latter quality. The wood has 
great torsional strength, excelling most of the soft 
woods in this respect, of coarse texture, close-grained 
and compact structure, takes a fine polish. Annual 
rings clearly marked, very durable in contact with 
the soil, shrinks and checks considerably in drying, 
the very narrow sapwood greenish yellow, the heart- 
wood brown, with shades of red and green. Used 
for wagon hubs, trenails or pins, but expecially for 
railway ties, fence posts, and door sills. Also used 
for boat parts, turnery, ornamentations, and locally 
for construction. Abroad it is much used for furni- 
ture and farming implements and also in turnery. At 
home in the Alleghany Mountains, extensively planted, 
especially in the West. 

52. Honey Locust (Gleditschia triacanthos) (Honey Shucks, 
Locust, Black Locust, Brown Locust, Sweet Locust, 
False Acacia, Three-Thorned Acacia). A medium- 
sized tree. Wood heavy, hard, strong, tough, durable 
in contact with the soil, of coarse texture, suscepti- 
ble to a good polish. The narrow sapwood yellow, 
the heartwood brownish red. So far, but Httle ap- 
preciated except for fences and fuel. Used to some 
extent for wheel hubs, and locally in rough con- 
struction. Found from Pennsylvania to Nebraska, 
and southward to Florida and Texas; locally quite 

53. Locust {Rohinia viscosa) (Clammy Locust). Usually 
a shrub five or six feet high, but known to reach a 
height of '40 feet in the mountains of North Carolina, 
with the habit of a tree. Wood light brown, heavy, 
hard, and close-grained. Not used to much extent 
in manufacture. Range same as the preceding. 



54. Magnolia {Magnolia glauca) (Swamp Magnolia, Small 
Magnolia, Sweet Bay, Beaver Wood). Small-sized 
tree. Heartwood reddish brown, sapwood cream 
white. Sparingly used in manufacture. Ranges from 
Essex County, Mass., to Long Island, N.Y., from 
New Jersey to Florida, and west in the Gulf region 
to Texas. 

55. Magnolia {Magnolia tripetala) (Umbrella Tree). A 
small-sized tree. Wood in its quality similiar to the 
preceding. It may be easily recognized by its great 
leaves, twelve to eighteen inches long, and five to 
eight inches broad. This species as well as the pre- 
ceding is an ornamental tree. Ranges from Pennsyl- 
vania southward to the Gulf. 

56. Cucumber Tree {Magnolia accuminata) (Tulip-wood, 
Poplar). Medium- to large-sized tree. Heartwood 
yellowish brown, sapwood almost white. Wood light, 
soft, satiny, close-grained, durable in contact with 
the soil, resembling and sometimes confounded with 
tulip tree {Liriodendron tuUpifera) in the markets. 
The wood shrinks considerably, but seasons without 
much injury, and works and stands well. It bends 
readily when steamed, and takes stain and paint well. 
Used in cooperage, for siding, for panelling and finish- 
ing lumber in house, car and shipbuilding, etc., also 
in the manufacture of toys, culinary woodenware, and 
backing for drawers. Most common in the southern 
Alleghanies, but distributed from western New York 
to southern Illinois, south through central Ken- 
tucky and Tennessee to Alabama, and throughout 


Wood heavy, hard, strong, stiff, and tough, of fine 
texture, frequently wavy-grained, this giving rise to 
''curly" and ''bhster" figures which are much admired. 
Not durable in the ground, or when exposed. Maple 


is creamy white, with shades of hght brown in the heart- 
wood, shrinks moderately, seasons, works, and stands well, 
wears smoothly, and takes a fine polish. The wood is 
used in cooperage, and for ceiling, flooring, panelling, 
stairway, and other finishing lumber in house, ship, and 
car construction. It is used for the keels of boats and ships, 
in the manufacture of implements and machinery, but 
especially for furniture, where entire chamber sets of 
maple rival those of oak. Maple is also used for shoe 
lasts and other form blocks; for shoe pegs; for piano 
actions, school apparatus, for wood type in show bill 
printing, tool handles, in wood carving, turnery, and 
scroll work, in fact it is one of our most useful woods. 
The maples are medium-sized trees, of fairly rapid growth, 
sometimes form forests, and frequently constitute a large 
proportion of the arborescent growth. They grow freely 
in parts of the Northern Hemisphere, and are particularly 
luxuriant in Canada and the northern portions of the 
United States. 

57. Sugar Maple {Acer saccharum) (Hard Maple, Rock 
Maple). Medium- to large-sized tree, very common, 
forms considerable forests, and is especially esteemed. 
The wood is close-grained, heavy, fairly hard and 
strong, of compact structure. Heartwood brownish, 
sap wood lighter color; it can be worked to a satin- 
like surface and take a fine polish, it is not durable 
if exposed, and requires a good deal of seasoning. 
Medullary rays small but distinct. The ''curly" 
or "wavy" varieties furnish wood of much beauty, 
the peculiar contortions of the grain called "bird's 
eye" being much sought after, and used as veneer for 
panelling, etc. It is used in all good grades of furni- 
ture, cabinetmaking, panelling, interior fiDish, and 
turnery; it is not liable to warp and twist. It is also 
largely used for flooring, for rollers for wringers and 
mangling machines, for which there is a large and 
increasing demand. The peculiarity known as "bird's 
eye," and which causes a difficulty in working the 
wood smooth, owing to the little pieces like knots 


lifting up, is supposed to be due to the action of boring 
insects. Its resistence to compression across the 
grain is higher than that of most other woods. Ranges 
from Maine to Minnesota, abundant, with birch, in 
the region of the Great Lakes. 

58. Red Maple {Acer ruhrum) (Swamp Maple, Soft 
Maple, Water Maple). Medium-sized tree. Like 
the preceding but not so valuable. Scattered along 
water-courses and other moist localities. Abundant, 
Maine to Minnesota, southward to northern Florida. 

59. Silver Maple {Acer saccharinum) (Soft Maple, White 
Maple, Silver-Leaved Maple). Medium- to large- 
sized tree, common. Wood lighter, softer, and in- 
ferior to Acer saccharum, and usually offered in small 
quantities and held separate in the markets. Heart- 
wood reddish brown, sapwood ivory white, fine- 
grained, compact structure. Fibres sometimes 
twisted, weaved, or curly. Not durable. Used in 
cooperage , for wooden ware, turnery articles, interior 
decorations and flooring. Valley of the Ohio, but 
occurs from Maine to Dakota and southward to 

60. Broad-Leaved Maple {Acer macrophyllum) (Oregon 
Maple). Medium-sized tree, forms considerable 
forests, and, like the preceding has a lighter, softer, 
and less valuable wood than Acer saccharum. Pacific 
Coast regions. 

61. Mountain Maple {Acer spicatum). Small-sized tree. 
Heartwood pale reddish brown, sapwood lighter color. 
Wood light, soft, close-grained, and susceptible of 
high polish. Ranges from lower St. Lawrence River 
to northern Minnesota and regions of the Saskatch- 
ewan River; south through the Northern States and 
along the Appalachian Mountains to Georgia. 

62. Ash-Leaved Maple {Acer negundo) (Box Elder). 
Medium- to large-sized tree. Heartwood creamy 
white, sapwood nearly white. Wood light, soft, close- 


grained, not strong. Used for woodenware and paper 
pulp. Distributed across the continent, abundant 
throughout the Mississippi Valley along banks of 
streams and borders of swamps. 

63. Striped Maple (Acer Pennsylvanicum) (Moose- wood). 
Small-sized tree. Produces a very white wood much 
sought after for inlaid and for cabinet work. Wood 
is light, soft, close-grained, and takes a fine polish. 
Not common. Occurs from Pennsylvania to Min- 


64. Red Mulberry (Morus rubra). A small-sized tree. 
Wood moderately heavy, fairly hard and strong, 
rather tough, of coarse texture, very durable in con- 
tact with the soil. The sapwood whitish, heartwood 
yellow to orange brown, shrinks and checks consider- 
ably in drying, works well and stands well. Used 
in cooperage and locally in construction, and in the 
manufacture of farm implements. Common in the 
Ohio and Mississippi Valleys, but widely distributed 
in the eastern United States. 

MYRTLE (See Laurel) 


Wood very variable, usually very heavy and hard, very 
strong and tough, porous, and of coarse texture. The 
sapwood whitish, the heartwood "oak" to reddish brown. 
It shrinks and checks badly, giving trouble in seasoning, 
but stands well, is durable, and little subject to the at- 
tacks of boring insects. Oak is used for many purposes, 
and is the chief wood used for tight cooperage; it is used 
in shipbuilding, for heavy construction, in carpentry, in 
furniture, car and wagon work, turnery, and even in wood- 
carving. It is also used in all kinds of farm implements, 
mill machinery, for piles and wharves, railway ties, etc., 
etc. The oaks are medium- to large-sized trees, forming 
the predominant part of a large proportion of our broad- 


leaved forests, so that these are generally termed "oak 
forests," though they always contain considerable pro- 
portion of other kinds of trees. Three well-marked kinds 
— white, red, and live oak — are distinguished and kept 
separate in the markets. Of the two principal kinds 
''white oak" is the stronger, tougher, less porous, and 
more durable. ''Red oak" is usually of coarser texture, 
more porous, often brittle, less durable, and even more 
troublesome in seasoning than white oak. In carpentry 
and furniture work red oak brings the same price at present 
as white oak. The red oaks everywhere accompany the 
white oaks, and, hke the latter, are usually represented 
by several species in any given locality. "Live oak," 
once largely employed in shipbuilding, possesses all the 
good qualities, except that of size, of white oak, even to 
a greater degree. It is one of the heaviest, hardest, tough- 
est, and most durable woods of this country. In structure 
it resembles the red oak, but is less porous. 

65. White Oak {Quercus alba) (American Oak) . Medium- 
to large-sized tree. Heartwood hght brown, 
sapwood hghter color. Annual rings well marked, 
medullary rays broad and prominent. Wood tough, 
strong, heavy, hard, liable to check in seasoning, 
durable in contact with the soil, takes a high pohsh, 
very elastic, does not shrink much, and can be bent 
to any form when steamed. Used for agricultural 
implements, tool handles, furniture, fixtures, in- 
terior finish, car and wagon construction, beams, 
cabinet work, tight cooperage, railway ties, etc., etc. 
Because of the broad medullary rays, it is generally 
"quarter-sawn" for cabinet work and furniture. 
Common in the Eastern States, Ohio and Mississippi 
Valleys. Occurs throughout the eastern United 

66. White Oak {Quercus durandii). Medium- to small- 
sized tree. Wood in its quality and uses similiar to 
the preceding. Texas, eastward to Alabama. 

67. White Oak {Quercus garryana) (Western White Oak). 
Medium- to large-sized tree. Stronger, more durable, 


and wood more compact than Quercus alba. Wash- 
ington to Cahfornia. 

68. White Oak (Quercus lobata). Medium- to large-sized 
tree. Largest oak on the Pacific Coast. Wood in 
its cjuahty and uses similar to Quercus alba, only it 
is finer-grained. California. 

69. Bur Oak (Quercus macrocarpa) (Mossy-Cup Oak, 
Over-Cup Oak). Large-sized tree. Heartwood "oak" 
brown, sapwood lighter color. Wood heavy, strong, 
close-grained, durable in contact with the soil. 
Used in ship- and boatbuilding, all sorts of con- 
struction, interior finish of houses, cabinet work, 
tight cooperage, carriage and wagon work, agricultural 
implements, railway ties, etc., etc. One of the most 
valuable and most widely distributed of American 
oaks, 60 to 80 feet in height, and, unlike most of the 
other oaks, adapts itself to varying climatic condi- 
tions. It is one of the most durable woods when in 
contact with the soil. Common, locally abundant. 
Ranges from Manitoba to Texas, and from the foot 
hills of the Rocky Mountains to the Atlantic Coast. 
It is the most abundant oak of Kansas and Nebraska, 
and forms the scattered forests known as "The oak 
openings" of Minnesota. 

70. Willow Oak (Quercus phellos) (Peach oak). Small 
to medium-sized tree. Heartwood pale reddish brown, 
sapwood lighter color. Wood heavy, hard, strong, 
coarse-grained. Occasionally used in construction. 
New York to Texas, and northward to Kentucky. 

71. Swamp White Oak (Quercus bicolor var. platanoides) . 
Large-sized tree. Heartwood pale brown, sapwood 
the same color. Wood heavy, hard, strong, tough, 
coarse-grained, checks considerably in seasoning. 
Used in construction, interior finish of houses, carriage- 
and boatbuilding, agricultural implements, in cooper- 
age, railway ties, fencing, etc., etc. Ranges from 
Quebec to Georgia and westward to Arkansas. Never 
abundant. Most abundant in the Lake States. 


72. Over-Cup Oak {Quercus lyrata) (Swamp White Oak, 
Swamp Post Oak). Medium to large-sized tree, 
rather restricted, as it grows in the swampy districts 
of Carohna and Georgia. Is a larger tree than most 
of the other oaks, and produces an excellent timber, 
but grows in districts difficult of access, and is not 
much used. Lower Mississippi and eastward to 

73. Pin Oak {Quercus palustris) (Swamp Spanish Oak, 
Water Oak). Medium- to large-sized tree. Heart- 
wood pale brown with dark-colored sapwood. Wood 
heavy, strong, and coarse-grained. Common along 
the borders of streams and swamps, attains its greatest 
size in the valley of the Ohio. Arkansas to Wiscon- 
sin, and eastward to the Alleghanies. 

74. Water Oak (Quercus aquatica) (Duck Oak, Possum 
Oak). Medium- to large-sized tree, of extremely 
rapid growth. Eastern Gulf States, eastward to 
Delaware and northward to Missouri and Kentucky. 

75. Chestnut Oak (Quercus prinus) (Yellow Oak, Rock 
Oak, Rock Chestnut Oak). Heartwood dark brown, 
sapwood Hghter color. Wood heavy, hard, strong, 
tough, close-grained, durable in contact with the soil. 
Used for railway ties, fencing, fuel, and locally for 
construction. Ranges from Maine to Georgia and 
Alabama, westward through Ohio, and southward 
to Kentucky and Tennessee. 

76. Yellow Oak (Quercus acuminata) (Chestnut Oak, 
Chinquapin Oak). Medium- to large-sized tree. 
Heartwood dark brown, sapwood pale brown. Wood 
heavy, hard, strong, close-grained, durable in con- 
tact with the soil. Used in the manufacture of wheel 
stock, in cooperage, for railway ties, fencing, etc., 
etc. Ranges from New York to Nebraska and east- 
ern Kansas, southward in the Atlantic region to the 
District of Columbia, and west of the Alleghanies 
southward to the Gulf States. 


77. Chinquapin Oak {Quercus prinoides) (Dwarf Chin- 
quapin Oak, Scrub Chestnut Oak). Small-sized tree. 
Heartwood light brown, sap wood darker color. Does 
not enter the markets to any great extent. Ranges 
from Massachusetts to North Carolina, westward to 
Missouri, Nebraska, Kansas, and eastern Texas. 
Reaches its best form in Missouri and Kansas. 

78. Basket Oak (Quercus michauxii) (Cow Oak), Large- 
sized tree. Locally abundant. Lower Mississippi 
and eastward to Delaware. 

79. Scrub Oak (Quercus ilicijolia var. pumila) (Bear Oak). 
Small-sized tree. Heartwood light brown, sapwood 
darker color. Wood heavy, hard, strong, and coarse- 
grained. Found in New England and along the 

80. Post Oak (Quercus ohtusiloda var. minor) (Iron Oak). 
Medium- to large-sized tree, gives timber of great 
strength. The color is of a brownish yellow hue, 
close-grained, and often superior to the white oak 
(Quercus alba) in strength and durability. It is used 
for posts and fencing, and locally for construction, 
Arkansas to Texas, eastward to New England and 
northward to Michigan. 

81. Red. Oak (Quercus rubra) (Black Oak). Medium- to 
large-sized tree. Heartwood light brown to red, sap- 
wood lighter color. Wood coarse-grained, well-marked 
annual rings, medullary rays few but broad. Wood 
heavy, hard, strong, liable to check in seasoning. 
It is found over the same range as white oak, and 
is more plentiful. Wood is spongy in grain, moder- 
ately durable, but unfit for work requiring strength. 
Used for agricultural implements, furniture, bob 
sleds, vehicle parts, boxes, cooperage, woodenware, 
fixtures, interior finish, railway ties, etc., etc. Com- 
mon in all parts of its range. Maine to Minnesota, 
and southward to the Gulf. 

82. Black Oak (Quercus tinctoria var. velutina) (Yellow 
Oak). Medium- to large-sized tree. Heartwood 


bright brown tinged with red, sapwood hghter color. 
Wood heavy, hard, strong, coarse-grained, checks 
considerably in seasoning. Very common in the 
Southern States, but occurring North as far as Min- 
nesota, and eastward to Maine. 

83. Barren Oak (Quercus nigra var. marilandica) (Black 
Jack, Jack Oak). Small-sized tree. Heartwood 
dark brown, sapwood lighter color. Wood heavy, 
hard, strong, coarse-grained, not valuable. Used 
in the manufacture of charcoal and for fuel. New 
York to Kansas and Nebraska, and southward to 
Florida. Rare in the North, but abundant in the 

84. Shingle Oak {Quercus imbricaria) (Laurel Oak). Small 
to medium-sized tree. Heartwood pale reddish 
brown, sapwood lighter color. Wood heavy, hard, 
strong, coarse-grained, checks considerably in dry- 
ing. Used for shingles and locally for construction. 
Rare in the east, most abundant in the lower Ohio 
Valley. From New York to Illinois and southward. 
Reaches its greatest size in southern Illinois and 

85. Spanish Oak {Quercus digitata var. falcata) (Red Oak) . 
Medium-sized tree. Heartwood light reddish brown, 
sapwood much lighter. Wood heavy, hard, strong, 
coarse-grained, and checks considerably in seasoning. 
Used locally for construction, and has high fuel value. 
Common in south Atlantic and Gulf region, but found 
from Texas to New York, and northward to Mis- 
souri and Kentucky. 

86. Scarlet Oak {Quercus coccinea). Medium- to large- 
sized tree. Heartwood light reddish-brown, sap- 
wood darker color. Wood heavy, hard, strong, and 
coarse-grained. Best developed in the lower basin 
of the Ohio, but found from Minnesota to Florida. 

87. Live Oak {Quercus virens) (Maul Oak). Medium- to 
large-sized tree. Grows from Maryland to the Gulf 


of Mexico, and often attains a height of 60 feet and 
4 feet in diameter. The wood is hard, strong, and 
durable, but of rather rapid growth, therefore not 
as good quahty as Quercus alba. The hve oak of 
Florida is now reserved by the United States Govern- 
ment for Naval purposes. Used for mauls and mal- 
lets, tool handles, etc., and locally for construction. 
Scattered along the coast from Maryland to Texas. 

88. Live Oak {Quercus chrysolepis) (Maul Oak, Valparaiso 
Oak). Medium- to small-sized tree. California. 


89. Osage Orange (Madura aurantiaca) (Bois d'Arc). 
A small-sized tree of fairly rapid growth. Wood 
very heavy, exceedingly hard, strong, not tough, of 
moderately coarse texture, and very durable and 
elastic. Sapwood yellow, heartwood brown on the 
end face, yellow on the longitudinal faces, soon 
turning grayish brown if exposed. It shrinks con- 
siderably in drying, but once dry it stands unusually 
well. Much used for wheel stock, and wagon framing; 
it is easily split, so is unfit for wheel hubs, but is very 
suitable for wheel spokes. It is considered one of 
the timbers likely to supply the place of black locust 
for insulator pins on telegraph poles. Seems too 
little appreciated; it is well suited for turned ware 
and especially for woodcarving. Used for spokes, 
insulator pins, posts, railway ties, wagon framing, 
turnery, and woodcarving. Scattered through the 
rich bottoms of Arkansas and Texas. 


90. Papaw (Asimina triloba) (Custard Apple). Small- 
sized tree, often only a shrub, Heartwood pale, 
yellowish green, sapwood lighter color. Wood light, 
soft, coarse-grained, and spongy. Not used to any 
extent in manufacture. Occurs in eastern and central 
Pennsylvania, west as far as Michigan and Kansas, 
and south to Florida and Texas. Often forming 


dense thickets in the lowlands bordering the Mis- 
sissippi River. 


91. Persimmon (Diospyros Virginiana) . Small to medium- 
sized tree. Wood very heavy, and hard, strong and 
tough; resembles hickory, but is of finer texture and 
elastic, but liable to split in working. The broad 
sapwood cream color, the heartwood brown, some- 
times almost black. The persimmon is the Virginia 
date plum, a tree of 30 to 50 feet high, and 18 to 20 
inches in diameter; it is noted chiefly for its fruit, 
but it produces a wood of considerable value. Used 
in turnery, for wood engraving, shuttles, bobbins, 
plane stock, shoe lasts, and largely as a substitute 
for box {Buxus sempervirens) — especially the black 
or Mexican variety, — also used for pocket rules and 
drawing scales, for flutes and other wind instru- 
ments. Common, and best developed in the lower 
Ohio Valley, but occurs from New York to Texas 
and Missouri. 

POPLAR (See also Tulip Wood) 

Wood light, very soft, not strong, of fine texture, and 
whitish, grayish to yellowish color, usually with a satiny 
luster. The wood shrinks moderately (some cross-grained 
forms warp excessively), but checks very little in season- 
ing; is easily worked, but is not durable. Used in cooper- 
age, for building and furniture lumber, for crates and 
boxes (especially cracker boxes), for wooden ware, and 
paper pulp. 

92. Cottonwood {Populus monilifera, var. angulata) (Caro- 
lina Poplar). Large-sized tree, forms considerable 
forests along many of the Western streams, and 
furnishes most of the Cottonwood of the market. 
Heartwood dark brown, sapwood nearly white. Wood 
light, soft, not strong, and close-grained (see Fig. 
14). Mississippi Valley and West. New England 
to the Rocky Mountains. 



93. Cottonwood {Populus fremontii var. wislizeni). Me- 
dium- to large-sized tree. Common. Wood in its 
quality and uses similiar to the preceding, but not 
so valuable. Texas to California. 

94. Black Cottonwood {Populus trichocarpa var. hetero- 
phylla) (Swamp Cottonwood, Downy Poplar). The 
largest deciduous tree of Washington. Very common. 

Fig. 14. A Large Cottonwood. One of the Associates of Red Gum. 


Heartwood dull brown, sapwood lighter brown. Wood 
soft, close-grained. Is now manufactured into lum- 
ber in the West and South, and used in interior finish 
of buildings. Northern Rocky Mountains and 
Pacific region. 

95. Poplar (Populus grandidentata) (Large-Toothed As- 
pen). Medium-sized tree. Heartwood light brown, 
sapwood nearly white. Wood soft and close-grained, 
neither strong nor durable. Chiefly used for wood 
pulp. Maine to Minnesota and southward along 
the Alleghanies. 

96. White Poplar {Populus alba) ( Abele-Tree) . Small 
to medium-sized tree. Wood in its quality and uses 
similar to the preceding. Found principally along 
banks of streams, never forming forests. Widely 
distributed in the United States. 

97. Lombardy Poplar {Populus nigra italica). Medium- 
to large-sized tree. This species is the first orna- 
mental tree introduced into the United States, and 
originated in Afghanistan. Does not enter into the 
markets. Widely planted in the United States. 

98. Balsam {Populus balsamifera) (Balm of Gilead, Tacma- 
hac). Medium- to large-sized tree. Heartwood light 
brown, sapwood nearly white. Wood light, soft, 
not strong, close-grained. Used extensively in the 
manufacture of paper pulp. Common all along the 
northern boundary of the United States. 

99.. Aspen {Populus tremuloides) (Quaking Aspen). Small 
to medium-sized tree, often forming extensive forests, 
and covering burned areas. Heartwood light brown, 
sapwood nearly white. Wood light, soft, close- 
grained, neither strong nor durable. Chiefly used 
for woodenware, cooperage, and paper pulp. Maine 
to Washington and northward, and south in the 
western mountains to California and New Mexico. 

RED GUM (See Gum) 



100. Sassafras {Sassafras sassafras). Medium-sized tree, 
largest in the lower Mississippi Valley. Wood light, 
soft, not strong, brittle, of coarse texture, durable 
in contact with the soil. The sapwood yellow, the 
heartwood orange brown. Used to some extent in 
slack cooperage, for skiff- and boatbuilding, fencing, 
posts, sills, etc. Occurs from New England to Texas 
and from Michigan to Florida. 

SOUR GUM (See Gum) 


101. Sourwood {Oxydendrum arhoreum) (Sorrel-Tree). A 
slender tree, reaching the maximum height of 60 feet. 
Heartwood reddish brown, sapwood lighter color. 

' Wood heavy, hard, strong, close-grained, and takes 
a fine polish. Ranges from Pennsylvania, along the 
AUeghanies, to Florida and Alabama, westward through 
Ohio to southern Indiana and southward through 
Arkansas and Louisiana to the Coast. 

SWEET GUM (See Gum) 


102. Sycam.ore (Platanus occidentalis) (Buttonwood, But- 
ton-Ball Tree, Plane Tree, Water Beech) . A large-sized 
tree, of rapid growth. One of the largest decidu- 
ous trees of the United States, sometimes attaining a 
height of 100 feet. It produces a timber that is mod- 
erately heavy, quite hard, stiff, strong, and tough, 
usually cross-grained; of coarse texture, difficult to 
split and work, shrinks moderately, but warps and 
checks considerably in seasoning, but stands well, 
and is not considered durable for outside work, or in 
contact with the soil. It has broad medullary rays, 
and much of the timber has a beautiful figure. It 
is used in slack cooperage, and quite extensively for 


drawers, backs, and bottoms, etc., in furniture work. 
It is also used for cabinet work, for tobacco boxes, 
crates, desks, flooring, furniture, ox-yokes, butcher 
blocks, and also for finishing lumber, where it has too 
long been underrated. Common and largest in the 
Ohio and Mississippi Valleys, at home in nearly all 
parts of the eastern United States. 

103. Sycamore (Platanus racemosa). The California 
species, resembUng in its wood the Eastern form. 
Not used to any great extent. 


104. Tulip Tree {Liriodendron tulipifera) (Yellow Poplar, 
Tuhp Wood, White Wood, Canary Wood, Poplar, 
Blue Poplar, White Poplar, Hickory Poplar). A 
medium- to large-sized tree, does not form forests, 
but is quite common, especially in the Ohio basin. 
Wood usuahy hght, but varies in weight, it is soft, 
tough, but not strong, of fine texture, and yellowish 
color. The wood shrinks considerably, but seasons 
without much injury, and works and stands extremely 
well. Heartwood hght yellow or greenish brown, 
the sapwood is thin, nearly white, and decays rapidly. 
The heartwood is fairly durable when exposed to the 
weather or in contact with the soil. It bends readily 
when steamed, and takes stain and paint well. The 
mature forest-grown tree has a long, straight, cyhndri- 
cal bole, clear of branches for at least two thirds of 
its length, surmounted by a short, open, irregular 
crown. When growing in the open, the tree main- 
tains a straight stem, but the crown extends almost 
to the ground, and is of conical shape. Yellow poplar, 
or tulip wood, ordinarily grows to a height of from 
100 to 125 feet, with a diameter of from 3 to 6 feet, 
and a clear length of about 70 feet. Trees have been 
found 190 feet high and ten feet in diameter. Used 
in cooperage, for siding, for panelhng and finishing 
lumber in houses, car- and shipbuilding, for sideboards, 
panels of wagons and carriages, for aeroplanes, 


for automobiles, also in the manufacture of furniture, 
farm implements, machinery, for pump logs, and 
almost every kind of common woodenware, boxes, 
shelving, drawers, etc., etc. Also in the manufacture 
of toys, culinary woodenware, and backing for veneer. 
It is in great demand throughout the vehicle and im- 
plement trade, and also makes a fair grade of wood 
pulp. In fact the tulip tree is one of the most use- 
ful of woods throughout the woodworking industry 
of this country. Occurs from New England to Mis- 
souri and southward to Florida. 

TUPELO (See Gum) 


105. Waahoo (Evonymus atropurpureus) (Burning Bush, 
Spindle Tree). A small-sized tree. Wood white, 
tinged with orange; heavy, hard, tough, and close- 
grained, works well and stands well. Used princi- 
pally for arrows and spindles. Widely distributed. 
Usually a shrub six to ten feet high, becoming a tree 
only in southern Arkansas and Oklahoma. 


106. Black Walnut (Juglans nigra) (Walnut). A large, 
beautiful, and quickly-growing tree, about 60 feet and 
upwards in height. Wood heavy, hard, strong, of 
coarse texture, very durable in contact with the soil. 
The narrow sapwood whitish, the heartwood dark, 
rich, chocolate brown, sometimes almost black; aged 
trees of fine quality bring fancy prices. The wood 
shrinks moderately in seasoning, works well and stands 
well, and takes a fine polish. It is quite handsome, 
and has been for a long time the favorite wood for 
cabinet and furniture making. It is used for gun- 
stocks, fixtures, interior decoration, veneer, panelling, 
stair newells, and all classes of work demanding 
a high priced grade of wood. Black walnut is 
a large tree with stout trunk, of rapid growth, and 


was formerly quite abundant throughout the Alle- 
ghany region. Occurs from New England to Texas, 
and from Michigan to Florida. Not common. 

WHITE WALNUT (See Butternut) 

WHITE WOOD (See Tulip and also Basswood) 

107. White Willow {Salix alba var. vitelUna) (Willow, 
Yellow Willow, Blue Willow). The wood is very 
soft, Hght, flexible, and fairly strong, is fairly durable 
in contact with the soil, works well and stands well 
when seasoned. Medium-sized tree, characterized 
by a short, thick trunk, and a large, rather irregular 
crown composed of many branches. The size of 
the tree at maturity varies with the locahty. In 
the region where it occurs naturally, a height of 70 
to 80 feet, and a diameter of three to four feet are 
often attained. When planted in the Middle West, 
a height of from 50 to 60 feet, and a diameter of one 
and one-half to two feet are all that may be expected. 
When closely planted on moist soil, the tree forms a 
tall, slender stem, well cleared branches. Is widely 
naturaUzed in the United States. It is used in cooper- 
age, for woodenware, for cricket and baseball bats, 
for basket work, etc. Charcoal made from the wood 
is used in the manufacture of gunpowder. It has 
been generally used for fence posts on the North- 
western plains, because of scarcity of better material. 
Well seasoned posts will last from four to seven 
years. Widely distributed throughout the United 

108. Black Willow (Salix nigra). Small-sized tree. 
Heartwood hght reddish brown, sapwood nearly 
white. Wood soft, hght, not strong, close-grained, 
and very flexible. Used in basket making, etc. 
Ranges from New York to Rocky Mountains and 
southward to Mexico. 


109. Shining Willow {Salix lucida). A small-sized tree. 
Wood in its quality and uses similiar to the preceding. 
Ranges from Newfoundland to Rocky Mountains, 
and southward to Pennsylvania and Nebraska. 

110. Perch Willow {Salix amygdaloides) (Almond-leaf 
Willow). Small to medium-sized tree. Heartwood 
light brown, sapwood lighter color. Wood light, 
soft, flexible, not strong, close-grained. Uses similiar 
to the preceding. Follows the water courses and 
ranges across the continent; less abundant in New 
England than elsewhere. Common in the West. 

111. Long-Leaf Willow (Salix fluviatilis) (Sand Bar Wil- 
low). A small-sized tree. Ranges from the Arctic 
Circle to Northern Mexico. 

112. Bebb Willow {Salix hebhiana var. rostrata). A small- 
sized tree. More abundant in British America than 
in the United States, where it ranges southward to 
Pennsylvania and westward to Minnesota. 

113. Glaucous Willow {Salix discolor) (Pussy Willow). 
A small-sized tree. Common along the banks of 
streams, and ranges from Novia Scota to Manitoba, 
and south to Delaware; west to Indiana and north- 
western Missouri. 

114. Crack Willow {Salix fragilis). A medium to large- 
sized tree. Wood is very soft, light, very flexible 
and fairly strong, is fairly durable in contact with 
the soil, works well and stands well. Used princi- 
pally for basket making, hoops, etc., and to pro- 
duce charcoal for gunpowder. Very common, and 
widely distributed in the United States. 

115. Weeping Willow {Salix hahylonica). Medium- to 
large-sized tree. Wood similiar to Salix nigra, but 
not so valuable. Mostly an ornamental tree. Origi- 
nally came from China. Widely planted in the 
United States. 



116. Yellow Wood (Cladrastis lutea) (Virgilia). A small 
to medium-sized tree. Wood yellow to pale brown, 
heavy, hard, close-grained and strong. Not used 
to much extent in manufacturing. Not common. 
Found principally on the limestone cliffs of Kentucky, 
Tennessee, and North Carohna. 




The terms "fine-grained," "coarse-grained," "straight- 
grained," and "cross-grained" are frequently applied in 
the trade. In common usage, wood is coarse-grained if 
its annual rings are wide; fine-grained if they are narrow. 
In the finer wood industries a fine-grained wood is capa- 
ble of high polish, while a coarse-grained wood is not, so 
that in this latter case the distinction depends chiefly on 
hardness, and in the former on an accidental case of slow 
or rapid growth. Generally if the direction of the wood 
fibres is parallel to the axis of the stem or limb in which 
they occur, the wood is straight-grained; but in many 
cases the course of the fibres is spiral or twisted around 
the tree (as shown in Fig. 15), and sometimes commonly 
in the butts of gum and cypress, the fibres of several layers 
are oblique in one direction, and those of the next series 
of layers are oblique in the opposite direction. (As shown 
in Fig. 16 the wood is cross or twisted grain.) Wavy- 
grain in a tangential plane as seen on the radial section is 
illustrated in Fig. 17, which represents an extreme case 
observed in beech. This same form also occurs on the 
radial plane, causing the tangential section to appear wavy 
or in transverse folds. 

When wavy grain is fine {i.e., the folds or ridges small 
but numerous) it gives rise to the "curly" structure 
frequently seen in maple. Ordinarily, neither wavy, 
spiral, nor alternate grain is visable on the cross-section; 
its existence often escapes the eje even on smooth, longi- 
tudinal faces in the sawed material, so that the only safe 



guide to their discovery lies in splitting the wood in two, 
in the two normal plaiks. 

Generally the surface of the wood under the bark, and 
therefore also that of any layer in the interior, is not uni- 


Fig 15 

Fig. 15. Spiral Grain. Season checks, after removal of bark, indicate the 

direction of the fibres or grain of the wood. 
Fig. 16. Alternating Spiral Grain in Cypress. Side and end view of same 

piece. When the bark was at o, the grain of this piece was straight. 

From that time, each year it grew more oblique in one direction, 

reaching a climax at a, and then turned back in the opposite direction. 

These alternations were repeated periodically, the bark sharing in 

these changes. 

form and smooth, but is channelled and pitted by numer- 
ous depressions, which differ greatly in size and form. 
Usually, any one depression or elevation is restricted to 
one or few annual layers {i.e., seen only in one or few rings) 
and is then lost, being compensated (the surface at the 
particular spot evened up) by growth. In some woods, 
however, any depression or elevation once attained grows 
from year to year and reaches a maximum size, which is 
maintained for many years, sometimes throughout life. 
In maple, where this tendency to preserve any particular 
contour is very great, the depressions and elevations are 


usually small (commonly less than one-eighth inch) but 
very numerous. 

On tangent boards of such wood, the sections, pits, and 
prominences appear as circlets, and give rise to the beauti- 
ful "bird's eye" or "landscape" structure. Similiar struct- 


4, ft. 


Fig. 17. Wavy Grain in Beech {after Nordlinger). 

ures in the burls of black ash, maple, etc., are frequently 
due to the presence of dormant buds, which cause the 
surface of all the layers through which they pass to be 
covered by small conical elevations, whose cross-sections 
on the sawed board appear as irregular circlets or islets, 
each with a dark speck, the section of the pith or "trace" 
of the dormant bud in the center. 

In the wood of many broad-leaved trees the wood fibres 
are much longer when full grown than when they are first 
formed in the cambium or growing zone. This causes 
the tips of each fibre to crowd in between the fibres above 
and below, and leads to an irregular interlacement of these 
fibres, which adds to the toughness, but reduces the cleava- 
bility of the wood. At the juncture of the limb and stem 
the fibres on the upper and lower sides of the limb behave 



differently. On the lower side they run from the stem 
into the limb, forming an uninterrupted strand or tissue 
and a perfect union. On the upper side the fibres bend 
aside, are not continuous into the 
limb, and hence the connection is 
not perfect (see Fig. 18). Owing 
to this arrangement of the fibres, 
the cleft made in splitting never 
runs into the knot if started on 
the side above the limb, but is 
apt to enter the knot if started 
below, a fact well understood in 
woodcraft. When limbs die, decay, 
and break off, the remaining stubs 
are surrounded, and may finally 
be covered by the growth of the 
trunk and thus give rise to the an- 
noying ''dead" or "loose" knots. 


Color, like structure, lends 
beauty to the wood, aids in its 
identification, and is of great value 
in the determination of its quality. 
If we consider only the heartwood, 
the black color of the persimmon, 
the dark brown of the walnut, the 
light brown of the white oaks, the 
reddish brown of the red oaks, 
the yellowish white of the tulip 
and poplars, the brownish red of 
the redwood and cedars, the yellow 
of the papaw and sumac, are all re- 
liable marks of distinction and color. 

Fig. 18. Section of Wood 
showing Position of the 
Grain at Base of a Limb. 
P, pith of both stem and 
limb; 1-7, seven yearly 
layers of wood; a, b, knot 
or basal part of a limb 
which lived for four years, 
then died and broke off 
near the stem, leaving the 
part to the left of a, b, a 
"sound" knot, the part 
to the right a "dead" 
knot, which would soon 
be entirely covered by 
the growing stem. 

Together with luster and weight, 
they are only too often the only features depended upon 
in practice. Newly formed wood, like that of the outer few 
rings, has but little color. The sapwood generally is hght, 


and the wood of trees which form no heartwood changes 
but httle, except when stained by forerunners of disease. 

The different tints of colors, whether the brown of oak, 
the orange brown of pine, the blackish tint of walnut, or 
the reddish cast of cedar, are due to pigments, while the 
deeper shade of the summer-wood bands in pine, cedar, 
oak, or walnut is due to the fact that the wood being 
denser, more of the colored wood substance occurs on a 
given space, i.e., there is more colored matter per square 
inch. Wood is translucent, a thin disk of pine permitting 
light to pass through quite freely. This translucency 
affects the luster and brightness of lumber. 

When lumber is attacked by fungi, it becomes more 
opaque, loses its brightness, and in practice is designated 
"dead," in distinction to "live" or bright timber. Ex- 
posure to air darkens all wood; direct sunlight and oc- 
casional moistening hasten this change, and cause it to 
penetrate deeper. Prolonged immersion has the same 
effect, pine wood becoming a dark gray, while oak changes 
to a blackish brown. 

Odor, like color, depends on chemical compounds, 
forming no part of the wood substance itself. Ex- 
posure to weather reduces and often changes the odor, 
but a piece of long-leaf pine, cedar, or camphor wood ex- 
hales apparently as much odor as ever when a new surface 
is exposed. Heartwood is more odoriferous than sapwood. 
Many kinds of wood are distinguished by strong and 
peculiar odors. This is especially the case with camphor, 
cedar, pine, oak, and mahogany, and the list would com- 
prise every kind of wood in use were our sense of smell 
developed in keeping with its importance. 

Decomposition is usually accompanied by pronounced 
odors. Decaying poplar emits a disagreeable odor, while 
red oak often becomes fragrant, its smell resembling that 
of heliotrope. 




A small cross-section of wood (as in Fig. 19) dropped 
into water sinks, showing that the substance of which 
wood fibre or wood is built up is heavier than water. By 
immersing the wood successively in 
heavier liquids, until we find a liquid 
in which it does not sink, and compar- 
ing the weight of the same with water, 
we find that wood substance is about 
1.6 times as heavy as water, and that 
this is as true of poplar as of oak or 

Separating a single cell (as shown in Fig. 19. Cross-section 
Fig. 20, a), drying and then dropping of a Group of Wood 
it into water, it floats. The air-filled ^^^^'g^^J^'^^^^ 
cell cavity or interior reduces its weight, ^^"^ 
and, hke an empty corked bottle, it weighs less than the 
water. Soon, however, water soaks into the cell, when it 
fills up and sinks. Many such cells grown to- 
j gether, as in a block of wood, when all or most 
of them are filled with water, will float as long 
as the majority of them are empty or only 
partially filled. This is why a green, sappy pine 
pole soon sinks in ''driving" (floating down 
stream). Its cells are largely filled before it is 
thrown in, and but little additional water suffices 
to make its weight greater than that of the 
water. In a good-sized white pine log, composed 
chiefly of empty cells (heartwood), the water 
requires a very long time to fifl up the cells (five 
years would not suffice to fifl them all), and 
therefore the log may float for many months. 
Fig. 20. When the wall of the wood fibre is very thick 
Isolated (f|yg eighths or more of the volume, as in Fig. 
20, h), the fibre sinks whether empty or filled. 
This applies to most of the fibres of the dark 
summer-wood bands in pines, and to the compact fibres 
of oak or hickory, and many, especiafly tropical woods, 


Fibres of 


have such thick-walled cells and so little empty or air space 
that they never float. 

Here, then, are the two main factors of weight in wood; 
the amount of cell wall or wood substance constant for 
any given piece, and the amount of water contained in 
the wood, variable even in the standing tree, and only in 
part eliminated in drying. 

The weight of the green wood of any species varies 
chiefly as a second factor, and is entirely misleading, if 
the relative weight of different kinds is sought. Thus 
some green sticks of the otherwise lighter cypress and 
gum sink more readily than fresh oak. 

The weight of sapwood or the sappy, peripheral part 
of our common lumber woods is always great, whether 
cut in winter or summer. It rarely falls much below 
forty-five pounds, and commonly exceeds fifty-five pounds 
to the cubic foot, even in our lighter wooded species. It 
follows that the green wood of a sapling is heavier than 
that of an old tree, the fresh wood from a disk of the upper 
part of a tree is often heavier than that of the lower part, 
and the wood near the bark heavier than that nearer the 
pith; and also that the advantage of drying the wood 
before shipping is most important in sappy and light 

When kiln-dried, the misleading moisture factor of 
weight is uniformly reduced, and a fair comparison pos- 
sible. For the sake of convenience in comparison, the 
weight of wood is expressed either as the weight per cubic 
foot, or, what is still more convenient, as specific weight 
or density. If an old long-leaf pine is cut up (as shown 
in Fig. 21) the wood of disk No. 1 is heavier than that of 
disk No. 2, the latter heavier than that of disk No. 3, and 
the wood of the top disk is found to be only about three 
fourths as heavy as that of disk No. 1. Similiarly, if disk 
No. 2 is cut up, as in the figure, the specific weight of the 
different parts is: 

a, about 0.52 

h, about 0.64 

c, about 0.67 

d, e, f, about 0.65 




showing that in this disk, at least 'the wood formed during 
the many years' growth, ^represented in piece a, is much 
lighter than that of former years. It also shows that the 
best wood is the middle part, with its large proportion of 
dark summer bands. 

Cutting up all disks in the same way, it will be found 
that the piece a of the first disk is heavier than the piece 
a of the fifth, and that piece c of the first disk excels the 

disc, 4f 




Fig. 21. Orientation of Wood Samples. 

piece c of all the other disks. This shows that the wood 
grown during the same number of years is lighter in the 
upper parts of the stem; and if the disks are smoothed on 
the radial surfaces and set up one on top of the other in 
their regular order, for the sake of comparison, this de- 
crease in weight will be seen to be accompanied by a de- 
crease in the amount of summer-wood. The color effect 
of the upper disks is conspicuously lighter. If our old 
pine had been cut one hundred and fifty years ago, 
before the outer, lighter wood was laid on, it is evident 
that the weight of the wood of any one disk would have 
been found to increase from the center outward, and no 
subsequent decrease could have been observed. 


In a thrifty young pine, then, the wood is heavier from 
the center outward, and lighter from below upward; only 
the wood laid on in old age falls in weight below the average. 
The number of brownish bands of summer-wood are a 
direct indication of these differences. If an old oak is 
cut up in the same manner, the butt cut is also found 
heaviest and the top lightest, but, unlike the disk of pine, 
the disk of oak has its firmest wood at the center, and each 
successive piece from the center outward is lighter than 
its neighbor. 

Examining the pieces, this difference is not as readily 
explained by the appearance of each piece as in the case 
of pine wood. Nevertheless, one conspicuous point ap- 
pears at once. The pores, so very distinct in oak, are 
very minute in the wood near the center, and thus the 
wood is far less porous. 

Studying different trees, it is found that in the pines, 
wood with narrow rings is just as heavy as and often heavier 
than the wood with wider rings; but if the rings are un- 
usually narrow in any part of the disk, the wood has a 
lighter color; that is, there is less summer-wood and there- 
fore less weight. 

In oak, ash, or elm trees of thrifty growth, the rings, 
fairly wide (not less than one- twelfth inch), always form 
the heaviest wood, while any piece with very narrow rings 
is light. On the other hand, the weight of a piece of hard 
maple or birch is quite independent of the width of its 

The bases of limbs (knots) are usually heavy, very 
heavy in conifers, and also the wood which surrounds 
them, but generally the wood of the limbs is lighter than 
that of the stem, and the wood of the roots is the 

In general, it may be said that none of the native woods 
in common use in this country are when dry as heavy as 
water, i.e., sixty-two pounds to the cubic foot. Few ex- 
ceed fifty pounds, while most of them fall below forty 
pounds, and much of the pine and other coniferous wood 
weigh less than thirty pounds per cubic foot. The weight 
of the wood is in itself an important quality. Weight 



assists in distinguishing maple from poplar. Lightness 
coupled with great strength and stiffness recommends 
wood for a thousand different uses. To a large extent 
weight predicates the strength of the wood, at least in the 
same species, so that a heavy piece of oak will exceed in 
strength a light piece of the same species, and in pine it 
appears probable that, weight for weight, the strength of 
the wood of various pines is nearly equal. 

Weight of Kiln-dried Wood of Different Species 


(a) Very Heavy Woods: 

Hickory, Oak, Persimmon, Osage Orange, 
Black Locust, Hackberry, Blue Beech, 
best of Elm and Ash 

(6) Heavy Woods: 

Ash, Elm, Cherry, Birch, Maple, Beech, 
Walnut, Sour Gum, Coffee Tree, Honey 
Locust, best of Southern Pine and 

(c) Woods of Medium Weight: 

Southern Pine, Pitch Pine, Tamarack, 
Douglas Spruce, Western Hemlock, 
Sweet Gum, Soft Maple, Sycamore, Sas- 
safras, Mulberry, light grades of Birch 
and Cherry 

(d) Light Woods: 

Norway and Bull Pine, Red Cedar, 
Cypress, Hemlock, the Heavier Spruces 
and Firs, Redwood, Basswood, Chestnut, 
Butternut, Tulip, Catalpa, Buckeye, 
heavier grades of Poplar 

(e) Very Light Woods: 

White Pine, Spruce, Fir, White Cedar, 



Weight of 










Foot Lumber 













Many theories have been propounded as to the cause 
of ''figure" in timber; while it is true that all timber 
possesses "figure" in some degree, which is more noticeable 
if it be cut in certain ways, yet there are some woods in 
which it is more conspicuous than in others, and which 
for cabinet or furniture work are much appreciated, as 
it adds to the value of the work produced. 

The characteristic "figure" of oak is due to the broad 
and deep medullary rays so conspicuous in this timber, 
and the same applies to honeysuckle. Figure due to the 
same cause is found in sycamore and beech, but is not so 
pronounced. The beautiful figure in "bird's eye maple" 
is supposed to be due to the boring action of insects in 
the early growth of the tree, causing pits or grooves, which 
in time become filled up by being overlain by fresh layers 
of wood growth; these peculiar and unique markings 
are found only in the older and inner portion of the tree. 

Pitch pine has sometimes a very beautiful ''figure," but 
it generally does not go deep into the timber; walnut has 
quite a variety of "figures," and so has the elm. It is in 
mahogany, however, that we find the greatest variety of 
"figure," and as this timber is only used for furniture and 
fancy work, a good "figure" greatly enhances its value, 
as firmly figured logs bring fancy prices. 

Mahogany, unlike the oak, never draws its "figure" from 
its small and almost unnoticeable medullary rays, but 
from the twisted condition of its fibres; the natural growth 
of mahogany produces a straight wood; what is called 
"figured" is unnatural and exceptional, and thus adds 
to its value as an ornamental wood. These peculiarities 
are rarely found in the earlier portion of the tree that is 
near the center, being in this respect quite different from 
maple; they appear when the tree is more fully developed, 
and consist of bundles of woody fibres which, instead of 
being laid in straight lines, behave in an erratic manner 
and are deposited in a twisted form; sometimes it may 
be caused by the intersection of branches, or possibly by 
the crackling of the bark pressing on the wood, and thus 


moving it out of its natural straight course, causing a 
wavy line which in time becomes accentuated. 

It will have been observed by most people that the outer 
portion of a tree is often indented by the bark, and the 
outer rings often follow a sinuous course which corresponds 
to this indention, but in most trees, after a few years, this 
is evened up and the annual rings assume their nearly 
circular form; it is supposed by some that in the case of 
mahogany this is not the case, and that the indentations 
are even accentuated. 

The best figured logs of timber are secured from trees 
which grow in firm rocky soil; those growing on low-lying 
or swampy ground are seldom figured. To the practical 
woodworker the figure in mahogany causes some difficulty 
in planing the wood to a smooth surface; some portions 
plane smooth, others are the "wrong way of the grain." 

Figure in wood is effected by the way light is thrown 
upon it, showing light if seen from one direction, and dark 
if viewed from another, as may easily be observed by hold- 
ing a piece of figured mahogany under artificial hght and 
looking at it from opposite directions. The character- 
istic markings on mahogany are "mottle," which is also 
found in sycamore, and is conspicuous on the backs of 
fiddles and violins, and is not in itself valuable; it runs 
the transverse way of the fibres and is probably the effect 
of the wind upon the tree in its early stages of growth. 
"Roe," which is said to be caused by the contortion of 
the woody fibres, and takes a wavy line parallel to them, 
is also found in the hollow of bent stems and in the root 
structure, and when combined with "mottle" is very 
valuable. "Dapple" is an exaggerated form of mottle. 
"Thunder shake," "wind shake," or "tornado shake" is 
a rupture of the fibres across the grain, which in mahogany 
does not always break them; the tree swaying in the wind 
only strains its fibres, and thus produces mottle in the wood. 



From the writer's personal investigations of this sub- 
ject in different sections of the country, the damage to 
forest products of various kinds from this cause seems 
to be far more extensive than is generally recognized. 
Allowing a loss of five per cent on the total value of the 
forest products of the country, which the writer believes 
to be a conservative estimate, it would amount to some- 
thing over $30,000,000 annually. This loss differs from 
that resulting from insect damage to natural forest re- 
sources, in that it represents more directly a loss of money 
invested in material and labor. In dealing with the in- 
sects mentioned, as with forest insects in general, the 
methods which yield the best results are those which relate 
directly to preventing attack, as well as those which are 
unattractive or unfavorable. The insects have two objects 
in their attack: one is to obtain food, the other is to pre- 
pare for the development of their broods. Different 
species of insects have special periods during the season 
of activity (March to November), when the adults are 
on the wing in search of suitable material in which to 
deposit their eggs. Some species, which fly in April, will 
be attracted to the trunks of recently felled pine trees or 
to piles of pine sawlogs from trees felled the previous 
winter. They are not attracted to any other kind of 
timber, because they can live only in the bark or wood 
of pine, and only in that which is in the proper condition 
to favor the hatching of their eggs and the normal de- 
velopment of their young. As they fly only in April, 
they cannot injure the logs of trees felled during the re- 
mainder of the year. 


There are also oak insects, which attack nothing but 
oak; hickory, cypress, and spruce insects, etc., which have 
different habits and different periods of flight, and require 
special conditions of the bark and wood for depositing 
their eggs or for subsequent development of their broods. 
Some of these insects have but one generation in a year, 
others have two or more, while some require more than 
one year for the complete development and transformation. 
Some species deposit their eggs in the bark or wood of 
trees soon after they are felled or before any perceptible 
change from the normal living tissue has taken place; 
other species are attracted only to dead bark and dead 
wood of trees which have been felled or girdled for several 
months; others are attracted to dry and seasoned wood; 
while another class will attack nothing but very old, dry 
bark or wood of special kinds and under special condi- 
tions. Thus it will be seen how important it is for the 
practical man to have knowledge of such of the foregoing 
facts as apply to his immediate interest in the manufacture 
or utilization of a given forest product, in order that he 
may with the least trouble and expense adjust his busi- 
ness methods to meet the requirements for preventing 

The work of different kinds of insects, as represented 
by special injuries to forest products, is the first thing to 
attract attention, and the distinctive character of this 
work is easily observed, while the insect responsible for 
it is seldom seen, or it is so difficult to determine by the 
general observer from descriptions or illustrations that 
the species is rarely recognized. Fortunately, the character 
of the work is often sufficient in itself to identify the cause 
and suggest a remedy, and in this section primary con- 
sideration is given to this phase of the subject. 

Ambrosia or Timber Beetles 

The characteristic work of this class of wood-boring 
beetles is shown in Figs. 22 and 23. The injury consists 
of pinhole and stained-wood defects in the sapwood and 
heartwood of recently felled or girdled trees, sawlogs, 
pulpwood, stave and shingle bolts, green or unseasoned 



Fig. 22. Work of Ambrosia Beetles in Tulip or Yellow Poplar Wood. 
a, work of Xyleborus affinis and Xylehorus inermis; b, Xyleborus obesus 
and work; c, bark; d, sapwood; e, heartwood. 

Fig. 23. Work of Ambrosia Beetles in Oak. a, Monarthrum mali aind work; 
b, Platypus compositus and work; c, bark; d, sapwood; e, heartwood; 
/, character of work in wood from injured log. 


lumber, and staves and heads of barrels containing alco- 
holic hquids. The holes and galleries are made by the 
adult parent beetles, to serve as entrances and temporary 
houses or nurseries for the development of their broods 
of young, which feed on a fungus growing on the walls of 
the galleries. 

The growth of this ambrosia-hke fungus is induced 
and controlled by the parent beetles, and the young are 
dependent upon it for food. The wood must be in ex- 
actly the proper condition for the growth of the fungus 
in order to attract the beetles and induce them to excavate 
their galleries; it must have a certain degree of moisture 
and other favorable qualities, which usually prevail during 
the period involved in the change from living, or normal, 
to dead or dry wood; such a condition is found in recently 
felled trees, sawlogs, or like crude products. 

There are two general types or classes of these galleries: 
one in which the broods develop together in the main 
burrows (see Fig. 22), the other in which the individuals 
develop in short, separate side chambers, extending at 
right angles from the primary galleries (see Fig. 23). The 
galleries of the latter type are usually accompanied by a 
distinct staining of the wood, while those of the former 
are not. 

The beetles responsible for this work are cyhndrical in 
form, apparently with a head (the prothorax) half as long 
as the remainder of the body (see Figs. 22, a, and 23, a). 

North American species vary in size from less than 
one-tenth to shghtly more than two-tenths of an inch, 
while some of the subtropical and tropical species attain 
a much larger size. The diameter of the holes made by 
each species corresponds closely to that of the body, and 
varies from about one-twentieth to one-sixteenth of an 
inch for the tropical species. 

Round-headed Borers 

The character of the work of this class of wood- and bark- 
boring grubs is shown in Fig. 24. The injuries consist 
of irregular flattened or nearly round wormhole defects 
in the wood, which sometimes result in the destruction 



of valuable parts of the wood or bark material. The sap- 
wood and heartwood of recently felled trees, sawlogs, 
poles, posts, mine props, pulpwood and cordwood, also 
lumber or square timber, with bark on the edges, and 
construction timber in new and old buildings, are injured 
by wormhole defects, while the valuable parts of stored 
oak and hemlock tanbark and certain kinds of wood are 
converted into worm-dust. These injuries are caused 
by the young or larvae of long-horned beetles. Those 
which infest the wood hatch from eggs deposited in the 

Fig. 24. Work of Round-headed and Flat-headed Borers in Pine, a, work 
of round-headed borer, "sawyer," Monohammus spiculatus, natural 
size; b, Er gates spiculatus; c, work of fiat-headed borer, Bwprestis, 
larva and adult; d, bark; e, sapwood; /, heartwood. 

outer bark of logs and like material, and the minute grubs 
hatching therefrom bore into the inner bark, through 
which they extend their irregular burrows, for the purpose 
of obtaining food from the sap and other nutritive material 
found in the plant tissue. They continue to extend and 
enlarge their burrows as they increase in size, until they 
are nearly or quite full grown. They then enter the wood 
and continue their excavations deep into the sapwood or 
heartwood until they attain their normal size. They 
then excavate pupa cells in which to transform into adults, 



which emerge from the wood through exit holes in the 
surface. This class of borers is represented by a large 
number of species. The adults, however, are seldom seen 
by the general observer unless cut out of the wood before 
they have energed. 

Flat-headed Borers 

The work of the flat-headed borers (Fig. 24) is only 
distinguished from that of the preceding by the broad, 
shallow burrows, and the much more oblong form of the 
exit holes. In general, the injuries are similiar, and effect 
the same class of products, but they are of much less im- 
portance. The adult forms are flattened, metaUic-colored 
beetles, and represent many species, of various sizes. 

Timber Worms 

The character of the work done by this class is shown 
in Fig. 25. The injury consists of pinhole defects in the 

Fig. 25. Work of Timber Worms in Oak. a, work of oak timber worm, 
Eupsalis minuta; b, barked surface; c, bark; d, sapwood timber worm, 
Hylocoetus lugubris, and work; e, sapwood. 

sapwood and heartwood of felled trees, sawlogs and hke 
material which have been left in the woods or in piles in the 
open for several months during the warmer seasons. Stave 



and shingle bolts and closely piled oak lumber and square 
timbers also suffer from injury of this kind. These in- 
juries are made by elongate, slender worms or larvae, 
which hatch from eggs deposited by the adult beetles in the 

Fig. 26. Work of Powder Post Beetle, Sinoxylon basilare, in Hickory Poles, 
showing Transverse Egg Galleries excavated by the Adult, a, entrance; 
b, gallery; c, adult. 

outer bark, or, where there is no bark, just beneath the 
surface of the wood. At first the young larvae bore 
almost invisible holes for a long distance through the sap- 
wood and heartwood, but as they increase in size the same 
holes are enlarged and extended until the larvae have at- 
tained their full growth. They then transform to adults, 
and emerge through the enlarged entrance burrows. The 

Fig. 27. Work of Powder Post Beetle, Sinoxylon basilare, in Hickory Pole. 
a, character of work by larvae; b, exit holes made by emerging broods. 

work of these timber worms is distinguished from that of 
the timber beetles by the greater variation in the size of 
holes in the same piece of wood, also by the fact that they 
are not branched from a single entrance or gallery, as are 
those made by the beetles. 



Powder Post Borers 

The character of the work of this class of insects is 
shown in Figs. 26, 27, and 28. The injury consists of 
closely placed burrows, packed 
with borings, or a completely 
destroyed or powdered condition 
of the wood of seasoned prod- 
ucts, such as lumber, crude and 
finished handle and wagon stock, 
cooperage and wooden truss 
hoops, furniture, and inside finish 
woodwork, in old buildings, as 
well as in many other crude or 
finished and utilized woods. 
This is the work of both the 
adults and young stages of some 
species, or of the larval stage 
alone of others. In the former, 
the adult beetles deposit their 
eggs in burrows or galleries ex- 
cavated for the purpose, as in 
Figs. 26 and 27, while in the ^_1 
latter (Fig. 28) the eggs are on 
or beneath the surface of the 
wood. The grubs complete the 
destruction by boring through 
the solid wood in all directions 
and packing their burrows with 
the powdered wood. When they 
are full grown they transform to ^'^ ^f: ^^°^k «^ ^^^^^^ P«^* 

, , , , , -, „ . , iseeties, Lyctus striatus, in 

the adult, and emerge from the Hickory Handles and Spokes. 

injured material through holes in 
the surface. Some of the species 
continue to work in the same 
wood until many generations 
have developed and emerged, or 
until every particle of wood 
tissue has been destroyed and the available nutritive sub- 
stance extracted. 

a, larva; h, pupa; c, adult; 
d, exit holes; e, entrance of 
larvae (vents for borings are 
exits of parasites); /, work 
of larvae; g, wood, com- 
pletely destroyed; h, sap- 
wood; i, heartwood. 


Conditions Favorable for Insect Injury — Crude Products 
— Round Timber with Bark on 

Newly felled trees, sawlogs, stave and heading bolts, 
telegraph poles, posts, and the like material, cut in the 
fall and winter, and left on the ground or in close piles 
during a few weeks or months in the spring or summer, 
causing them to heat and sweat, are especially liable to 
injury by ambrosia beetles (Figs. 22 and 23), round and 
flat-headed borers (Fig. 24), and timber worms (Fig. 25), 
as are also trees felled in the warm season, and left for a 
time before working up into lumber. 

The proper degree of moisture found in freshly cut 
living or dying wood, and the period when the insects are 
flying, are the conditions most favorable for attack. This 
period of danger varies with the time of the year the timber 
is felled and with the different kinds of trees. Those 
felled in late fall and winter will generally remain at- 
tractive to ambrosia beetles, and to the adults of round- 
and flat-headed borers during March, April, and May. 
Those felled in April to September may be attacked in 
a few days after they are felled, and the period of danger 
m.ay not extend over more than a few weeks. Certain 
kinds of trees felled during certain months and seasons 
are never attacked, because the danger period prevails 
only when the insects are flying; on the other hand, if 
the same kinds of trees are felled at a different time, the 
conditions may be most attractive when the insects are 
active, and they will be thickly infested and ruined. 

The presence of bark is absolutley necessary for in- 
festation by most of the wood-boring grubs, since the eggs 
and young stages must occupy the outer and inner por- 
tions before they can enter the wood. Some ambrosia 
and timber worms will, however, attack barked logs, 
especially those in close piles, and others shaded and 
protected from rapid drying. 

The sapwood of pine, spruce, fir, cedar, cypress, and 
the like softwoods is especially liable to injury by ambrosia 
beetles, while the heartwood is sometimes ruined by a 
class of round-headed borers, known as ''sawyers." Yellow 


poplar, oak, chestnut, gum, hickory, and most other 
hardwoods are as a rule attacked by species of ambrosia 
beetles, sawyers, and timber worms, different from those 
infesting the pines, there being but very few species which 
attack both. 

Mahogany and other rare and valuable woods imported 
from the tropics to this country in the form of round logs, 
with or without bark on, are commonly damaged more 
or less seriously by ambrosia beetles and timber worms. 

It would appear from the writer's investigations of 
logs received at the mills in this country, that the prin- 
cipal damage is done during a limited period — from the 
time the trees are felled until they are placed in fresh or 
salt water for transportation to the shipping points. If, 
however, the logs are loaded on a vessel direct from the 
shore, or if not left in the water long enough to kill the 
insects, the latter will continue their destructive work 
during transportation to other countries and after they 
arrive, and until cold weather ensues or the logs are con- 
verted into lumber. 

It was also found that a thorough soaking in sea-water, 
while it usually killed the insects at the time, did not pre- 
vent subsequent attacks by both foreign and native ambro- 
sia beetles; also, that the removal of the bark from such 
logs previous to immersion did not render them entirely 
immune. Those with the bark off were attacked more 
than those with it on, owing to a greater amount of saline 
moisture retained by the bark. 

How to Prevent Injury 

From the foregoing it will be seen that some requisites 
for preventing these insect injuries to round timber are: 

1. To provide for as little delay as possible between 
the felling of the tree and its manufacture into 
rough products. This is especially necessary with 
trees felled from April to September, in the region 
north of the Gulf States, and from March to Novem- 
ber in the latter, while the late fall and winter 
cutting should all be worked up by March or April. 


2. If the round timber must be left in the woods or on 

the skidways during the danger period, every pre- 
caution should be taken to facilitate rapid drying 
of the inner bark, by keeping the logs off the ground, 
in the sun, or in loose piles; or else the opposite 
extreme should be adopted and the logs kept in 

3. The immediate removal of all the bark from poles, 

posts, and other material which will not be seri- 
ously damaged by checking or season checks. 

4. To determine and utilize the proper months or sea- 

sons to girdle or fell different kinds of trees: Bald 
cypress in the swamps of the South are "girdled" 
in order that they may die, and in a few weeks or 
months dry out and become light enough to float. 
This method has been extensively adopted in sec- 
tions where it is the only practicable one by which 
the timber can be transported to the sawmills. 
It is found, however, that some of these "girdled'^ 
trees are especially attractive to several species of 
ambrosia beetles (Figs. 22 and 23), round-headed 
borers (Fig. 24) and timber worms (Fig. 25), which 
cause serious injury to the sap wood or heartwood, 
while other trees "girdled" at a different time or 
season are not injured. This suggested to the 
writer the importance of experiments to determine 
the proper time to "girdle" trees to avoid losses, and 
they are now being conducted on an extensive 
scale by the United States Forest Service, in co- 
operation with prominent cypress operators in 
different sections of the cypress-growing region. 


Saplings, including hickory and other round hoop-poles 
and similiar products, are subject to serious injuries and 
destruction by round- and flat-headed borers (Fig. 24), 
and certain species of powder post borers (Figs. 26 and 27) 
before the bark and wood are dead or dry, and also by 
other powder post borers (Fig. 28) after they are dried and 


seasoned. The conditions favoring attack by the former 
class are those resulting from leaving the poles in piles 
or bundles in or near the forest for a few weeks during the 
season of insect activity, and by the latter from leaving 
them stored in one place for several months. 

Stave, Heading and Shingle Bolts 

These are attacked by ambrosia beetles (Figs. 22 and 
23), and the oak timber worm (Fig. 25, a), which, as has 
been frequently reported, cause serious losses. The con- 
ditions favoring attack by these insects are similiar to 
those mentioned under "Round Timber." The insects 
may enter the wood before the bolts are cut from the log 
or afterward, especially if the bolts are left in moist, shady 
places in the woods, in close piles during the danger period. 
If cut during the warm season, the bark should be re- 
moved and the bolts converted into the smallest practic- 
able size and piled in such manner as to facilitate rapid 

Unseasoned Products in the Rough 

Freshly sawn hardwood, placed in close piles during 
warm, damp weather in July and September, presents 
especially favorable conditions for injury by ambrosia 
beetles (Figs. 22, a, and 23, a). This is due to the con- 
tinued moist condition of such material. 

Heavy two-inch or three-inch stuff is also liable to at- 
tack even in loose piles with lumber or cross sticks. An 
example of the latter was found in a valuable lot of ma- 
hogany lumber of first grade, the value of which was 
reduced two thirds by injury from a native ambrosia 
beetle. Numerous complaints have been received from 
different sections of the country of this class of injury to 
oak, poplar, gum, and other hardwoods. In all cases it 
is the moist condition and retarded drying of the lumber 
which induces attack; therefore, any method which wiU 
provide for the rapid drying of the wood before or after 
piling will tend to prevent losses. 

It is important that heavy lumber should, as far as 
possible, be cut in the winter months and piled so that it 


will be well dried out before the middle of March. Square 
timber, stave and heading bolts, with the bark on, often 
suffer from injuries by flat- or round-headed borers, hatch- 
ing from eggs deposited in the bark of the logs before they 
are sawed and piled. One example of serious damage 
and loss was reported in which white pine staves for paint 
buckets and other small wooden vessels, which had been 
sawed from small logs, and the bark left on the edges, 
were attacked by a round-headed borer, the adults having 
deposited their eggs in the bark after the stock was sawn , 
and piled. The character of the injury is shown in Fig. 29. ^yLy 
Another example was reported from a manufacturer in 
the South, where the pieces of lumber which har strips 
of bark on one side were seriously damaged by the same 
kind of borer, the eggs having been deposited in the logs 
before sawing or in the bark after the lumber was piled. 
If the eggs are deposited in the logs, and the borers have 
entered the inner bark or the wood before sawing, they 
may continue their work regardless of methods of piling, 
but if such lumber is cut from new logs and placed in the 
pile while green, with the bark surface up, it will be much 
less liable to attack than if piled with the bark edges down. 
This liability of lumber with bark edges or sides to be 
attacked by insects suggests the importance of the re- 
moval of the bark, to prevent damage, or, if this is not 
practicable, the lumber with the bark on the sides should 
be piled in open, loose piles with the bark up, while that 
with the bark on the edges should be placed on the outer 
edges of the piles, exposed to the light and air. 

In the Southern States it is difficult to keep green timber 
in the woods or in piles for any length of time, because of 
the rapidity which wood-destroying fungi attack it. This 
is particularly true daring the summer season, when the 
humidity is greatest. There is really no easily-applied, 
general specific for these summer troubles in the handling 
of wood, but there are some suggestions that are worth 
while that it may be well to mention. One of these, and 
the most important, is to remove all the bark from the 
timber that has been cut, just as soon as possible after 
felling. And, in this, emphasis should be laid on the all. 



as a piece of bark no larger than a man's little finger will 
furnish an entering place for insects, and once they get in, 
it is a difficult matter to get rid of them, for they seldom 
stop boring until they ruin the stick. And again, after 

Fig. 29. Work of Round-headed Borers, Callidium antennatum, in White 
Pine Bucket Staves from New Hampshire, a, where egg was deposited 
in bark; h, larval mine; c, pupal cell; d, exit in bark; e, adult. 

the timber has been felled and the bark removed, it is 
well to get it to the mill pond or cut up into merchantable 
sizes and on to the pile as soon as possible. What is 
wanted is to get the timber up off the ground, to a 
place where it can get plenty of air, to enable the sap 
to dry up before it sours; and, besides, large units of 
wood are more likely to crack open on the ends from the 


heat than they would if cut up into the smaller units 
for merchandizing. 

A moist condition of lumber and square timber, such 
as results from close or solid piles, with the bottom layers 
on the ground or on foundations of old decaying logs or 
near decaying stumps and logs, offers especially favorable 
conditions for the attack of white ants. 

Seasoned Products in the Rough 

Seasoned or dry timber in stacks or storage is liable to 
injury by powder post borers (Fig. 28). The condi- 
tions favoring attack are: (1) The presence of a large 
proportion of sapwood, as in hickory, ash, and similiar 
woods; (2) material which is two or more years old, or 
that which has been kept in one place for a long time; 
(3) access to old infested material. Therefore, such stock 
should be frequently examined for evidence of the presence 
of these insects. This is always indicated by fine, flour- 
like powder on or beneath the piles, or otherwise associated 
with such material. All infested material should be at 
once removed and the infested parts destroyed by burning. 

Dry Cooperage Stock and Wooden Truss Hoops 
These are especially liable to attack and serious injury 
by powder post borers (Fig. 28), under the same or similiar 
conditions as the preceding. 

Staves and Heads of Barrels containing 
Alcoholic Liquids 

These are liable to attack by ambrosia beetles (Figs. 
22, a, and 23, a), which are attracted by the moist con- 
dition and possibly by the peculiar odor of the wood, re- 
sembling that of dying sapwood of trees and logs, which 
is their normal breeding place. 

There are many examples on record of serious losses 
of liquors from leakage caused by the beetles boring through 
the staves and heads of the barrels and casks in cellars 
and storerooms. 

The condition, in addition to the moisture of the wood, 
which is favorable for the presence of the beetles, is prox- 


imity to their breeding places, such as the trunks and 
stumps of recently felled or dying oak, maple, and other 
hardwood or deciduous trees; lumber yards, sawmills, 
freshly-cut cordwood, from living or dead trees, and forests 
of hardwood timber. Under such conditions the beetles 
occur in great numbers, and if the storerooms and cellars 
in which the barrels are kept stored are damp, poorly venti- 
lated, and readily accessible to them, serious injury is 
almost certain to follow. 




Local Distribution of Water in Wood 

As seasoning means essentially the more or less rapid 
evaporation of water from wood, it will be necessary to 
discuss at the very outset where water is found in wood, 
and its local seasonal distribution in a tree. 

Water may occur in wood in three conditions: (1) It 
forms the greater part (over 90 per cent) of the proto- 
plasmic contents of the living cells; (2) it saturates the 
walls of all cells; and (3) it entirely or at least partly fills 
the cavities of the lifeless cells, fibres, and vessels. 

In the sapwood of pine it occurs in all three forms; in 
the heartwood only in the second form, it merely saturates 
the walls. 

Of 100 pounds of water associated with 100 pounds of 
dry wood substance taken from 200 pounds of fresh sap- 
wood of white pine, about 35 pounds are needed to saturate 
the cell walls, less than 5 pounds are contained in the 
living cells, and the remaining 60 pounds partly fill the 
cavities of the wood fibres. This latter forms the sap 
as ordinarily understood. 

The wood next to the bark contains the most water. 
In the species which do not form heartwood, the decrease 
toward the pith is gradual, but where heartwood is formed 
the change from a more moist to a drier condition is usually 
quite abrupt at the sapwood limit. 

In long-leaf pine, the wood of the outer one inch of a 
disk may contain 50 per cent of water, that of the next, 
or the second inch, only 35 per cent, and that of the heart- 


wood, only 20 per cent. In such a tree the amount of 
water in any one section varies with the amount of sap- 
wood, and is greater for the upper than the lower cuts, 
greater for the limbs than the stems, and greatest of all 
in the roots. 

Different trees, even of the same kind and. from the 
same place, differ as to the amount of water they contain. 
A thrifty tree contains more water than a stunted one, 
and a young tree more than on old one, while the wood 
of all trees varies in its moisture relations with the season 
of the year. 

Seasonal Distribution of Water in Wood 

It is generally supposed that trees contain less water 
in winter than in summer. This is evidenced by the 
popular saying that "the sap is down in the winter." This 
is probably not always the case; some trees contain as 
much water in winter as in summer, if not more. Trees 
normally contain the greatest amount of water during 
that period when the roots are active and the leaves are 
not yet out. This activity commonly begins in January, 
February, and March, the exact time varying with the 
kind of timber and the local atmospheric conditions. And 
it has been found that green wood becomes lighter or 
contains less water in late spring or early summer, when 
transpiration through the foliage is most rapid. The 
amount of water at any one season, however, is doubtless 
much influenced by the amount of moisture in the soil. 
The fact that the bark peels easily in the spring depends 
on the presence of incomplete, soft tissue found between 
wood and bark during this season, and has little to do 
with the total amount of water contained in the wood of 
the stem. 

Even in the living tree a flow of sap from a cut occurs 
only in certain kinds of trees and under special circum- 
stances. From boards, felled timber, etc., the water 
does not flow out, as is sometimes believed, but must be 
evaporated. The seeming exceptions to this rule are 
mostly referable to two causes; clefts or "shakes" will 


allow water contained in them to flow out, and water is 
forced out of sound wood, if very sappy, whenever the 
wood is warmed, just as water flows from green wood when 
put in a stove. 

Composition of Sap 

The term "sap" is an ambiguous expression. The 
sap in the tree descends through the bark, and except 
in early spring is not present in the wood of the tree 
except in the medullary rays and living tissues in the 

What flows through the "sap wood" is chiefly water 
brought from the soil. It is not pure water, but contains 
many substances in solution, such as mineral salts, and 
in certain species — maple, birch, etc., it also contains 
at certain times a small percentage of sugar and other 
organic matter. 

The water rises from the roots through the sapwood to 
the leaves, where it is converted into true "sap" which 
descends through the bark and feeds the living tissues 
between the bark and the wood, which tissues make the 
annual growth of the trunk. The wood itself contains 
very little true sap and the heartwood none. 

The wood contains, however, mineral substances, or- 
ganic acids, volatile oils and gums, as resin, cedar oil, etc. 

All the conifers — pines, cedars, junipers, cypresses, 
sequoias, yews, and spruces — contain resin. The sap 
of deciduous trees — those which shed their leaves at 
stated seasons — is lacking in this element, and its con- 
stituents vary greatly in the different species. But there 
is one element common to all trees, and for that matter 
to almost all plant growth, and that is albumen. 

Both resin and albumen, as they exist in the sap of 
woods, are soluble in water; and both harden with heat, 
much the same as the white of an egg, which is almost 
pure albumen. 

These organic substances are the dissolved reserve food, 
stored during the winter in the pith rays, etc., of the wood 
and bark; generally but a mere trace of them is to be 
found. From this it appears that the solids contained 


in the sap, such as albumen, gum, sugar, etc., cannot 
exercise the influence on the strength of the wood which is 
so commonly claimed for them. 

Effects of Moisture on Wood 

The question of the effect of moisture upon the strength 
and stiffness of wood offers a wide scope for study, and 
authorities consulted differ in conclusions. Two authori- 
ties give the tensile strength in pounds per square inch 
for white oak as 10,000 and 19,500, respectively; for 
spruce, 8,000 to 19,500, and other species in similiar start- 
ling contrasts. 

Wood, we are told, is composed of organic products. 
The chief material is cellulose, and this in its natural state 
in the living plant or green wood contains from 25 to 35 
per cent of its weight in moisture. The moisture renders 
the cellulose substance pliable. What the physical action 
of the water is upon the molecular structure of organic 
material, to render it softer and more pliable, is largely 
a matter of conjecture. 

The strength of a timber depends not only upon its 
relative freedom from imperfections, such as knots, crooked- 
ness of grain, decay, wormholes or ring-shakes, but also 
upon its density; upon the rate at which it grew, and 
upon the arrangement of the various elements which 
compose it. 

The factors effecting the strength of wood are therefore 
of two classes: (1) Those inherent in the wood itself and 
which may cause differences to exist between two pieces 
from the same species of wood or even between the two 
ends of a piece, and (2) those which are foreign to the wood 
itself, such as moisture, oils, and heat. 

Though the effect of moisture is generally temporary, 
it is far more important than is generally realized. So 
great, indeed, is the effect of moisture that under some 
conditions it outweighs all the other causes which effect 
strength, with the exception, perhaps of decided imper- 
fections in the wood itself. 


The Fibre Saturation Point in Wood 

Water exists in green wood in two forms: (1) As liquid 
water contained in the cavities of the cells or pores, and 
(2) as "imbibed" water intimately absorbed in the sub- 
stance of which the wood is composed. The removal of 
the free water from the cells or pores will evidently have 
no effect upon the physical properties or shrinkage of the 
wood, but as soon as any of the "imbibed" moisture is 
removed from the cell walls, shrinkage begins to take place 
and other changes occur. The strength also begins to 
increase at this time. 

The point where the cell walls or wood substance be- 
comes saturated is called the "fibre saturation point," 
and is a very significant point in the drying of wood. 

It is easy to remove the free water from woods which 
will stand a high temperature, as it is only necessary to 
heat the wood slightly above the boiling point in a closed 
vessel, which will allow the escape of the steam as it is 
formed, but will not allow dry air to come in contact with 
the wood, so that the surface will not become dried below 
its saturation point. This can be accomplished with 
most of the softwoods, but not as a rule with the hard- 
woods, as they are injured by the temperature necessary. 

The chief difficulties are encountered in evaporating 
the ''imbibed" moisture and also where the free water 
has to be removed through its gradual transfusion instead 
of boiling. As soon as the imbibed moisture begins to 
be extracted from any portion, shrinkage takes place and 
stresses are set up in the wood which tend to cause checking. 

The fibre saturation point lies between moisture con- 
ditions of 25 and 30 per cent of the dry weight of the 
wood, depending on the species. Certain species of eu- 
calyptus, and probably other woods, however, appear to 
be exceptional in this respect, in that shrinkage begins 
to take place at a moisture condition of 80 to 90 per cent 
of the dry weight. 


WHAT SEA80]sri]^G 18 

Seasoning is ordinarily understood to mean drying. 
When exposed to the sun and air, the water in green wood 
rapidly evaporates. The rate of evaporation will depend 
on: (1) the kind of wood; (2) the shape and thickness of 
the timber; and (3) the conditions under which the wood 
is placed or piled. 

Pieces of wood completely surrounded by air, exposed 
to the wind and the sun, and protected by a roof from 
rain and snow, will dry out very rapidly, while wood piled 
or packed close together so as to exclude the air, or left 
in the shade and exposed to rain and snow, will dry out 
very slowly and will also be subject to mould and decay. 

But seasoning implies other changes besides the evapora- 
tion of water. Although we have as yet only a vague 
conception as to the exact nature of the difference between 
seasoned and unseasoned wood, it is very probable that 
one of these consists in changes in the albuminous sub- 
stances in the wood fibres, and possibly also in the tannins, 
resins, and other incrusting substances. Whether the 
change in these substances is merely a drying-out, or 
whether it consists in a partial decomposition is at yet 
undetermined. That the change during the seasoning 
process is a profound one there can be no doubt, because 
experience has shown again and again that seasoned wood 
fibre is very much more permeable, both for liquids and 
gases than the living, unseasoned fibre. 

One can picture the albuminous substances as forming 
a coating which dries out and possibly disintegrates when 
the wood dries. The drying-out may result in consider- 
able shrinkage, which may make the wood fibre more 
porous. It is also possible that there are oxidizing in- 


fluences at work within these substances which result in 
their disintegration. Whatever the exact nature of the 
change may be, one can say without hesitation that ex- 
posure to the wind and air brings about changes in the 
wood, which are of such a nature that the wood becomes 
drier and more permeable. 

When seasoned by exposure to live steam, similiar 
changes may take place; the water leaves the wood in the 
form of steam, while the organic compounds in the walls 
probably coagulate or disintegrate under the high tem- 

The most effective seasoning is without doubt that 
obtained by the uniform, slow drying which takes place 
in properly constructed piles outdoors, under exposure 
to the winds and the sun and under cover from the rain 
and snow, and is what has been termed "air-seasoning." 
By air-seasoning oak and similiar hardwoods, nature per- 
forms certain functions that cannot be duplicated by any 
artificial means. Because of this, woods of this class 
cannot be successfully kiln-dried green from the saw. 

In drying wood, the free water within the cells passes 
through the cell walls until the cells are empty, while the 
cell walls remain saturated. When all the free water has 
been removed, the cell walls begin to yield up their mois- 
ture. Heat raises the absorptive power of the fibres and 
so aids the passage of water from the interior of the cells. 
A confusion in the word ''sap" is to be found in many 
discussions of kiln-drying; in some instances it means 
water, in other cases it is applied to the organic substances 
held in a water solution in the cell cavities. The term is 
best confined to the organic substances from the living 
cell. These substances, for the most part of the nature 
of sugar, have a strong attraction for water and water 
vapor, and so retard drying and absorb moisture into 
dried wood. High temperatures, especially those pro- 
duced by live steam, appear to destroy these organic com- 
pounds and therefore both to retard and to limit the 
reabsorption of moisture when the wood is subsequently 
exposed to the atmosphere. 

Air-dried wood, under ordinary atmospheric tempera- 


tures, retains from 10 to 20 per cent of moisture, whereas 
kiln-dried wood may have no more than 5 per cent as it 
comes from the kiln. The exact figures for a given species 
depend in the first case upon the weather conditions, and 
in the second case upon the temperature in the kiln and 
the time during which the wood is exposed to it. When 
wood that has been kiln-dried is allowed to stand in the 
open, it apparently ceases to reabsorb moisture from the 
air before its moisture content equals that of wood which 
has merely been air-dried in the same place, and under 
the same conditions, in other words kiln-dried wood will 
not absorb as much moisture as air-dried wood under the 
same conditions. 

Difference between Seasoned and Unseasoned Wood 

Although it has been known for a long time that there 
is a marked difference in the length of life of seasoned and 
of unseasoned wood, the consumers of wood have shown 
very little interest in its seasoning, except for the purpose 
of doing away with the evils which result from checking, 
warping, and shrinking. For this purpose both kiln- 
drying and air-seasoning are largely in use. 

The drying of material is a subject which is extremely 
important to most industries, and in no industry is it of 
more importance than in the lumber trade. Timber 
drying means not only the extracting of so much water, 
but goes very deeply into the quality of the wood, its 
workability and its cell strength, etc. 

Kiln-drying, which dries the wood at a uniformly rapid 
rate by artificially heating it in inclosed rooms, has be- 
come a part of almost every woodworking industry, as 
without it the construction of the finished product would 
often be impossible. Nevertheless much unseasoned or 
imperfectly seasoned wood is used, as is evidenced by the 
frequent shrinkage and warping of the finished articles. 
This is explained to a certain extent by the fact that the 
manufacturer is often so hard pressed for his product that 
he is forced to send out an inferior article, which the con- 
sumer is willing to accept in that condition rather than 


to wait several weeks or months for an article made up 
of thoroughly seasoned material, and also that dry kilns 
are at present constructed and operated largely without 
thoroughgoing system. 

Forms of kilns and mode of operation have commonly 
been copied by one woodworking plant after the example of 
some neighboring establishment. In this way it has been 
brought about that the present practices have many short- 
comings. The most progressive operators, however, have 
experimented freely in the effort to secure special results 
desirable for their peculiar products. Despite the diversity 
of practice, it is possible to find among the larger and more 
enterprising operators a measiu-e of agreement, as to both 
methods and results, and from this to outline the essentials 
of a correct theory. As a result, properly seasoned wood 
commands a high price, and in some cases cannot be ob- 
tained at all. 

Wood seasoned out of doors, which by many is supposed 
to be much superior to kiln-dried material, is becoming 
very scarce, as the demand for any kind of wood is so great 
that it is thought not to pay to hold it for the time nec- 
essary to season it properly. How long this state of affairs 
is going to last it is difficult to say, but it is believed that 
a reaction wiU come when the consumer learns that in 
the long run it does not pay to use poorly seasoned material. 
Such a condition has now arisen in connection with another 
phase of the seasoning of wood ; it is a commonly accepted 
fact that dry wood will not decay nearly so fast as wet 
or green wood; nevertheless, the immense superiority of 
seasoned over unseasoned wood for all purposes where 
resistance to decay is necessary has not been sufficiently 
recognized. In the times when wood of all kinds was 
both plentiful and cheap, it mattered little in most cases 
how long it lasted or resisted decay. Wood used for 
furniture, flooring, car construction, cooperage, etc., usually 
got some chance to dry out before or after it was placed 
in use. The wood which was exposed to decaying in- 
fluences was generally selected from those woods which, 
whatever their other qualities might be, would resist de- 
cay longest. 


To-day conditions have changed, so that wood can no 
longer be used to the same extent as in former years. 
Inferior woods with less lasting qualities have been pressed 
into service. Although haphazard methods of cutting 
and subsequent use are still much in vogue, there are 
many signs that both lumbermen and consumers are 
awakening to the fact that such carelessness and waste- 
ful methods of handling wood will no longer do, and must 
give way to more exact and economical methods. The 
reason why many manufacturers and consumers of wood 
are still using the older methods is perhaps because of 
long custom, and because they have not yet learned that, 
though the saving to be obtained by the application of 
good methods has at all times been appreciable, now, 
when wood is more valuable, a much greater saving is 
possible. The increased cost of applying economical 
methods is really very slight, and is many times exceeded 
by the value of the increased service which can be secured 
through its use. 

Manner of Evaporation of Water 

The evaporation of water from wood takes place largely 
through the ends, i.e., in the direction of the longitudinal 
axis of the wood fibres. The evaporation from the other 
surfaces takes place very slowly out of doors, and with 
greater rapidity in a dry kiln. The rate of evaporation 
differs both with the kind of timber and its shape; that is, 
thin material will dry more rapidly than heavier stock. 
Sapwood dries faster than heartwood, and pine more 
rapidly than oak or other hardwoods. 

Tests made show httle difference in the rate of evapora- 
tion in sawn and hewn stock, the results, however, not 
being conclusive. Air-drying out of doors takes from 
two months to a year, the time depending on the kind of 
timber, its thickness, and the climatic conditions. After 
wood has reached an air-dry condition it absorbs water 
in small quantities after a rain or during damp weather, 
much of which is immediately lost again when a few warm, 
dry days follow. In this way wood exposed to the weather 



will continue to absorb water and lose it for indefinite 

When soaked in water, seasoned woods absorb water 
rapidly. This at first enters into the wood through the 
cell walls; when these are soaked, the water will fill the 
cell lumen, so that if constantly submerged the wood may 
become completely filled with water. 

The following figures show the gain in weight by ab- 
sorption of several coniferous woods, air-dry at the start, 
expressed in per cent of the kiln-dry weight : 

Absorption of Water by Dry Wood 

White Pine 

Red Cedar 










In water 1 day 


In water 2 days 

In water 3 days 


In water 4 days 


In water 5 days 


In water 7 days 

In water 9 days 

In water 11 days 

In water 14 days 

In water 17 days 

In water 25 days 


In water 30 days 


Rapidity of Evaporation 

The rapidity with which water is evaporated, that is, 
the rate of drying, depends on the size and shape of the 
piece and on the structure of the wood. An inch board 
dries more than four times as fast as a four-inch plank, and 
more than twenty times as fast as a ten-inch timber. 
White pine dries faster than oak. A very moist piece of 
pine or oak will, during one hour, lose more than four times 
as much water per square inch from the cross-section, but 
only one half as much from the tangential as from the radial 
section. In a long timber, where the ends or cross-sec- 
tions form but a small part of the drying surface, this dif- 


ference is not so evident. Nevertheless, the ends dry 
and shrink first, and being opposed in this shrinkage by 
the more moist adjoining parts, they check, the cracks 
largely disappearing as seasoning progresses. 

High temperatures are very effective in evaporating 
the water from wood, no matter how humid the air, and 
a fresh piece of sapwood may lose weight in boiling water, 
and can be dried to quite an extent in hot steam. 

In drying chemicals or fabrics, all that is required is to 
provide heat enough to vaporize the moisture and circu- 
lation enough to carry off the vapor thus secured, and the 
quickest and most economical means to these ends may 
be used. While on the other hand, in drying wood, whether 
in the form of standard stock or the finished product, the 
application of the requisite heat and circulation must be 
carefully regulated throughout the entire process, or 
warping and checking are almost certain to result. More- 
wood of different shapes and thicknesses is very dif- 
ferently^'^ffected by the same treatment. Finally, the 
tissues composing the wood, which vary in form and physi- 
cal properties, and which cross each other in regular direc- 
tions, exert their own peculiar influences upon its behavior 
during drying. With our native woods, for instance, 
summer-wood and spring-wood show distinct tendencies 
in drying, and the same is true in a less degree of heart- 
wood, as contrasted with sapwood. Or, again, pronounced 
medullary rays further complicate the drying problem. 

Physical Properties that influence Drying 

The principal properties which render the drying of 
wood peculiarly difficult are: (1) The irregular shrinkage; 
(2) the different ways in which water is contained; (3) the 
manner in which moisture transfuses through the wood 
from the center to the surface; (4) the plasticity of the 
wood substance while moist and hot; (5) the changes 
which take place in the hygroscopic and chemical nature 
of the surface ; and (6) the difference produced in the total 
shrinkage by different rates of drying. 

The shrinkage is unequal in different directions and 
in different portions of the same piece. It is greatest in 


the circumferential direction of the tree, being generally 
twice as great in this direction as in the radial direction. 
In the longitudinal direction, for most woods, it is almost 
negligible, being from 20 to over 100 times as great cir- 
cumferentially as longitudinally. 

There is a great variation in different species in this 
respect. Consequently, it follows from necessity that 
large internal strains are set up when the wood shrinks, 
and were it not for its plasticity it would rupture. There 
is an enormous difference in the total amount of shrinkage 
of different species of wood, varying from a shrinkage of 
only 7 per cent in volume, based on the green dimensions, 
in the case of some of the cedars to nearly 50 per cent in 
the case of some species of eucalyptus. 

When the free water in the capillary spaces of the wood 
fibre is evaporated it follows the laws of evaporation from 
capillary spaces, except that the passages are not all free 
passages, and much of the water has to pass out by a 
process of transfusion through the moist cell walls. These 
cell walls in the green wood completely surround the cell 
cavities so that there are no openings large enough to offer 
a passage to water or air. 

The well-known "pits" in the cell walls extend through 
the secondary thickening only, and not through the pri- 
mary walls. This statement applies to the tracheids and 
parenchyma cells in the conifer (gymnosperms), and to the 
tracheids, parenchyma cells, and the wood fibres in the 
broad-leaved trees (angiosperms) ; the vessels in the latter, 
however, form open passages except when clogged by 
ingrowth called tyloses, and the resin canals in the former 
sometimes form occasional openings. 

By heating the wood above the boiling point, correspond- 
ing to the external pressure, the free water passes through 
the cell walls more readily. 

To remove the moisture from the wood substance re- 
quires heat in addition to the latent heat of evaporation, 
because the molecules of moisture are so intimately as- 
sociated with the molecules, minute particles composing 
the wood, that energy is required to separate them there- 
from. / 


.fPrT^fnl ^^V'^^^te^ experiments show this to be from 
16.6 to 19.6 calories per grain of dry wood in the case of 
beech, long-leaf pme, and sugar maple. 

^^^^'^'!!'i*^ imposed in drying, however, is not so 
much the additional heat required as it is in the rate at 
which the water transfuses through the sohd wood 



Three most important advantages of seasoning have 
already been made apparent: 

1. Seasoned timber lasts much longer than unseasoned. 

Since the decay of timber is due to the attacks of 
wood-destroying fungi, and since the most important 
condition of the growth of these fungi is water, 
anything which lessens the amount of water in 
wood aids in its preservation. 

2. In the case of treated timber, seasoning before treat- 

ment greatly increases the effectiveness of the 
ordinary methods of treatment, and seasoning after 
treatment prevents the rapid leaching out of the 
salts introduced to preserve the timber. 

3. The saving in freight where timber is shipped from 

one place to another. Few persons realize how 
much water green wood contains, or how much it 
will lose in a comparatively short time. Experi- 
ments along this line with lodge-pole pine, white 
oak, and chestnut gave results which were a surprise 
to the companies owning the timber. 

Freight charges vary considerably in different parts of 
the country; but a decrease of 35 to 40 per cent in weight 
is important enough to deserve everywhere serious con- 
sideration from those in charge of timber operations. 

When timber is shipped long distances over several 
roads, as is coming to be more and more the case, the sav- 
ing in freight will make a material difference in the cost 
of lumber operations, irrespective of any other advantages 
of seasoning. 


Prevention of Checking and Splitting 

Under present methods much timber is rendered unfit 
for use by improper seasoning. Green timber, particu- 
larly when cut during January, February, and March, 
when the roots are most active, contains a large amount 
of water. When exposed to the sun and wind or to high 
temperatures in a drying room, the water will evaporate 
more rapidly from the outer than from the inner parts 
of the piece, and more rapidly from the ends than from 
the sides. As the water evaporates, the wood shrinks, 
and when the shrinkage is not fairly uniform the wood 
cracks and splits. 

When wet wood is piled in the sun, evaporation goes 
on with such unevenness that the timbers split and crack 
in some cases so badly as to become useless for the purpose 
for which it was intended. Such uneven drying can be 
prevented by careful piling, keeping the logs immersed 
in a log pond until wanted, or by piling or storing under 
an open shed so that the sun cannot get at them. 

Experiments have also demonstrated that injury to 
stock in the way of checking and splitting always de- 
velops immediately after the stock is taken into the dry 
kiln, and is due to the degree of humidity being too low. 

The receiving end of the kiln should always be kept 
moist, where the stock has not been steamed before being 
put into the kiln, as when the air is too dry it tends to 
dry the outside of the stock first — which is termed "case- 
hardening" — and in so doing shrinks and closes up the 
pores. As the material is moved down the kiln (as 
in the case of ''progressive kilns"), it absorbs a 
continually increasing amount of heat, which tends 
to drive off the moisture still present in the center of 
the piece, the pores on the outside having been closed 
up, there is no exit for the vapor or steam that is being 
rapidly formed in the center of the piece. It must find 
its way out in some manner, and in doing so sets up strains, 
which result either in checking or splitting. If the hu- 
midity had been kept higher, the outside of the piece would 
not have dried so quickly, and the pores would have re- 


mained open for the exit of the moisture from the in- 
terior of the piece, and this trouble would have been 
avoided. (See also article following.) 

Shrinkage of Wood 

Since in all our woods, cells with thick walls and cells 
with thin walls are more or less intermixed, and especially 
as the spring-wood and summer-wood nearly always differ 
from each other in this respect, strains and tendencies 
to warp are always active when wood dries out, because 
the summer-wood shrinks more than the spring-wood, 
and heavier wood in general shrinks more than light wood 
of the same kind. 

If a thin piece of wood after drjdng is placed upon a 
moist surface, the cells on the under side of the piece take 
up moisture and swell before the upper cells receive any 
moisture. This causes the under side of the piece to be- 
come longer than the upper side, and as a consequence 
warping occurs. Soon, however, the moisture penetrates 
to all the cells and the piece straightens out. But while 
a thin board of pine curves laterally it remains quite 
straight lengthwise, since in this direction both shrinkage 
and swelling are small. If one side of a green board is 
exposed to the sun, warping is produced by the removal of 
water and consequent shrinkage of the side exposed; this 
may be eliminated by the frequent turning of the topmost 
pieces of the piles in order that they may be dried evenly. 

As already stated, wood loses water faster from the 
ends than from the longitudinal faces. Hence the ends 
shrink at a different rate from the interior parts. The 
faster the drying at the surface, the greater is the difference 
in the moisture of the different parts, and hence the greater 
the strains and consequently also the greater amount of 
checking. This becomes very evident when freshly cut 
wood is placed in the sun, and still more when put into a 
hot, dry kiln. While most of these smaller checks are only 
temporary, closing up again, some large radial checks re- 
main and even grow larger as drying progresses. Their 
cause is a different one and will presently be explained. 
The temporary checks not only appear at the ends, but 


are developed on the sides also, only to a much smaller 
degree. They become especially annoying on the surface 
of thick planks of hardwoods, and also on peeled logs 
when exposed to the sun. 

So far we have considered the wood as if made up only 
of parallel fibres all placed longitudinally in the log. 
This, however, is not the case. A large part of the wood 
is formed by the medullary or pith rays. In pine over 
15,000 of these occur on a square inch of a tangential 
section, and even in oak the very large rays, which are 
readily visible to the eye, represent scarcely a hundredth 
part of the number which a microscope reveals, as the 
cells of these rays have their length at right angles to the 
direction of the wood fibres. 

If a large pith ray of white oak is whittled out and al- 
lowed to dry, it is found to shrink greatly in its width, 
while, as we have stated, the fibres to which the ray is 
firmly grown in the wood do not shrink in the same direc- 
tion. Therefore, in the wood, as the cells of the pith ray 
dry they pull on the longitudinal fibres and try to shorten 
them, and, being opposed by the rigidity of the fibres, the 
pith ray is greatly strained. But this is not the only 
strain it has to bear. Since the fibres shrink as much 
again as the pith ray, in this its longitudinal direction, 
the fibres tend to shorten the ray, and the latter in op- 
posing this prevents the former from shrinking as much 
as they otherwise would. 

Thus the structure is subjected to two severe strains 
at right angles to each other, and herein lies the greatest 
difficulty of wood seasoning, for whenever the wood dries 
rapidly these fibres have not the chance to "give" or ac- 
comodate themselves, and hence fibres and pith rays 
separate and checking results, which, whether visible or 
not7^9 detrimental in the use of the wood. 

The contraction of the pith rays parallel to the length 
of the board is probably one of the causes of the small 
amount of longitudinal shrinkage which has been ob- 
served in boards. This smaller shrinkage of the pith 
rays along the radius of the log (the length of the pith ray), 
opposing the shrinkage of the fibres in this direction, be- 


comes one of the causes of the second great trouble in 
wood seasoning, namely, the difference in the shrinkage 
along the radius and that along the rings or tangent. This 
greater tangential shrinkage appears to be due in part to 
the causes just mentioned, but also to the fact that the 
greatly shrinking bands of summer-wood are interrupted 
along the radius by as many bands of porous spring-wood, 
while they are continuous in the tangential direction. In 
this direction, therefore, each such band tends to shrink, 
as if the entire piece were composed of summer-wood, 
and since the summer-wood represents the greater part 
of the wood substance, this greater tendency to tangential 
shrinkage prevails. > 

The effect of this greater tangential shrinkage effects 
every phase of woodworking. It leads to permanent 
checks and causes the log or piece to split open on drying. 
Sawed in two, the flat sides of the log become convex; 
sawed into timber, it checks along the median line of 
the four faces, and if converted into boards, the latter 
checks considerably from the end through the center, all 
owing to the greater tangential shrinkage of the wood. 

Briefly, then, shrinkage of wood is due to the fact that 
the cell walls grow thinner on drying. The thicker cell 
walls and therefore the heavier wood shrinks most, while 
the water in the cell cavities does not influence the volume 
of the wood. 

Owing to the great difference of cells in shape, size, and 
thickness of walls, and still more in their arrangement, 
shrinkage is not uniform in any kind of wood. This 
irregularity produces strains, which grow with the dif- 
ference between adjoining cells and are greatest at the 
pith rays. These strains cause warping and checking, 
but exist even where no outward signs are visible. They 
are greater if the wood is dried rapidly than if dried slowly, 
but can never be entirely avoided. 

Temporary checks are caused by the more rapid dry- 
ing of the outer parts of any stick; permanent checks 
are due to the greater shrinkage, tangentially, along the 
rings than along the radius. This, too, is the cause of 
most of the ordinary phenomena of shrinkage, such as 


the difference in behavior of the entire and quartered logs, 
''bastard" (tangent) and rift (radial) boards, etc., and 
explains many of the phenomena erroneously attributed 
to the influence of bark, or of the greater shrinkage of 
outer and inner parts of any log. 

Once dry, wood may be swelled again to its original 
size by soaking in water, boihng, or steaming. Soaked 
pieces on drying shrink again as before; boiled and steamed 
pieces do the same, but to a slightly less degree. Neither 
hygroscopicity, i.e., the capacity of taking up water, nor 
shrinkage of wood can be overcome by drying at tempera- 
tures below 200 degrees Fahrenheit. Higher temperatures, 
however, reduce these quahties, but nothing short of a 
coahng heat robs wood of the capacity to shrink and swell. 

Rapidly dried in a kiln, the wood of oak and other 
hardwoods "case-harden," that is, the outer part dries 
and shrinks before the interior has a chance to do the same, 
and thus forms a firm shell or case of shrunken, commonly 
checked wood around the interior. This shell does not 
prevent the interior from drying, but when this drying 
occurs the interior is commonly checked along the medul- 
lary rays, commonly called "honeycombing" or "hollow- 
horning." In practice this occurrence can be prevented 
by steaming or sweating the wood in the kiln, and still 
better by drying the wood in the open air or in a shed 
before placing in the kiln. Since only the first shrinkage 
is apt to check the wood, any kind of lumber which has 
once been air-dried (three to six months for one-inch stuff) 
may be subjected to kiln heat without any danger from 
this source. 

Kept in a bent or warped condition during the first 
shrinkage, the wood retains the shape to which it has 
been bent and firmly opposes any attempt at subsequent 

Sapwood, as a rule, shrinks more than heartwood of 
the same weight, but very heavy heartwood may shrink 
more than hghter sapwood. The amount of water in 
wood is no criterion of its shrinkage, since in wet wood 
most of the water is held in the cavities, where it has no 
effect on the volume. 


The wood of pine, spruce, cypress, etc., with its very 
regular structure, dries and shrinks evenly, and suffers 
much less in seasoning than the wood of broad-leaved 
(hardwood) trees. Among the latter, oak is the most 
difficult to dry without injury. 

Desiccating the air with certain chemicals will cause the 
wood to dry, but wood thus dried at 80 degrees Fahrenheit 
will still lose water in the kiln. Wood dried at 120 degrees 
Fahrenheit loses water still if dried at 200 degrees Fahren- 
heit, and this again will lose more water if the temperature 
be raised, so that absolutely dry wood cannot be obtained, 
and chemical destruction sets in before all the water is 
driven off. 

On removal from the kiln, the dry wood at once takes 
up moisture from the air, even in the driest weather. At 
first the absorption is quite rapid; at the end of a week 
a short piece of pine, 1| inches thick, has regained two 
thirds of, and, in a few months, all the moisture which it 
had when air-dry, 8 to 10 per cent, and also its former 
dimensions. In thin boards all parts soon attain the 
same degree of dryness. In heavy timbers the interior re- 
mains more moist for many months, and even years, than 
the exterior parts. Finally an equilibrium is reached, 
and then only the outer parts change with the weather. 

With kiln-dried woods all parts are equally dry, and 
when exposed, the moisture coming from the air must 
pass through the outer parts, and thus the order is re- 
versed. Ordinary timber requires months before it is 
at its best. Kiln-dried timber, if properly handled, is 
prime at once. 

Dry wood if soaked in water soon regains its original 
volume, and in the heartwood portion it may even sur- 
pass it; that is to say, swell to a larger dimension than 
it had when green. With the soaking it continues to 
increase in weight, the cell cavities filling with water, and 
if left many months all pieces sink. Yet after a year's 
immersion a piece of oak 2 by 2 inches and only 6 inches 
long still contains air; i.e., it has not taken up all the 
water it can. By rafting or prolonged immersion, wood 
loses some of its weight, soluble materials being leached 


out, but it is not impaired either as fuel or as building 
material. Immersion, and still more boiling and steam- 
ing, reduce the hygroscopicity of wood and therefore also 
the troublesome "working," or shrinking and sweUing. 
Exposure in dry air to a temperature of 300 degrees Fah- 
renheit for a short time reduces but does not destroy the 
hygroscopicity, and with it the tendency to shrink and 
swell. A piece of red oak which has been subjected to a 
temperature of over 300 degrees Fahrenheit still swells in 
hot water and shrinks in a dry kiln. 

Expansion of Wood 

It must not be forgotten that timber, in common with 
every other material, expands as well as contracts. If 
we extract the moisture from a piece of wood and so cause 
it to shrink, it may be swelled to its original volume by 
soaking it in water, but owing to the protection given to 
most timber in dwelling-houses it is not much affected by 
wet or damp weather. The shrinkage is more apparent, 
more lasting, and of more consequence to the architect, 
builder, or owner than the slight expansion which takes 
place, as, although the amount of moisture contained in 
wood varies with the climate conditions, the consequence 
of dampness or moisture on good timber used in houses 
only makes itself apparent by the occasional jamming of a 
door or window in wet or damp weather. 

Considerable expansion, however, takes place in the 
wood-paving of streets, and when this form of paving 
was in its infancy much trouble occurred owing to all 
allowances not having been made for this contingency, 
the trouble being doubtless increased owing to the blocks 
not being properly seasoned; curbing was lifted or pushed 
out of hne and gully grids were broken by this action. As 
a rule in street paving a space of one or two inches wide 
is now left next to the curb, which is filled with sand or 
some soft material, so that the blocks may expand longitu- 
dinally without injuring the contour or affecting the curbs. 
But even with this arrangement it is not at all unusual 
for an inch or more to have to be cut off paving blocks 
parallel to the channels some time after the paving has 


been laid, owing to the expansion of the wood exceeding 
the amounts allowed. 

Considerable variation occurs in the expansion of wood 
blocks, and it is noticeable in the hardwoods as well as in 
the softwoods, and is often greater in the former than in 
the latter. 

Expansion takes place in the direction of the length of 
the blocks as they are laid across the street, and causes 
no trouble in the other direction, the reason being that 
the lengthway of a block of wood is across the grain of 
the timber, and it expands or contracts as a plank does. 
On one occasion, in a roadway forty feet wide, expansion 
occurred until it amounted to four inches on each side, 
or eight inches in all. This continual expansion and con- 
traction is doubtless the cause of a considerable amount of 
wood street-paving bulging and becoming filled with 
ridges and depressions. 

Elimination of Stain and Mildew 

A great many manufacturers, and particularly those 
located in the Southern States, experience a great amount 
of difficulty in their timber becoming stained and mil- 
dewed. This is particularly true with gum wood, as it will 
frequently stain and mould in twenty-four hours, and 
they have experienced so much of this trouble that they 
have, in a great many instances, discontinued cutting it 
during the summer season. 

If this matter were given proper attention they should 
be able to eliminate a great deal of this difficulty, as no 
doubt they will find after investigation that the mould 
has been caused by the stock being improperly piled to 
the weather. 

Freshly sawn wood, placed in close piles during warm, 
damp weather in the months of July and August, presents 
especially favorable conditions for mould and stain. In 
all cases it is the moist condition and retarded drying of 
the wood which causes this. Therefore, any method which 
will provide for the rapid drying of the wood before or 
after piling will tend to prevent the difficulty, and the 
best method for eliminating mould is (1) to provide for 


as little delay as possible between the felling of the tree, 
and its manufacture into rough products before the sap 
has had an opportunity of becoming sour. This is es- 
pecially necessary with trees felled from April to Septem- 
ber, in the region north of the Gulf States, and from March 
to November in the latter, while the late fall and winter 
cutting should all be worked up by March or April. (2) 
The material should be piled to the weather immediately 
after being sawn or cut, and every precaution should be 
taken in piling to facilitate rapid drying, by keeping the 
piles or ricks up off the ground. (3) All weeds (and em- 
phasis should be placed on the all) and other vegeta- 
tion should be kept well clear of the piles, in order that the 
air may have a clear and unobstructed passage through and 
around the piles, and (4) the piles should be so constructed 
that each stick or piece will have as much air space about 
it as it is possible to give to it. 

If the above instructions are properly carried out, there 
will be little or no difficulty experienced with mould ap- 
pearing on the lumber. 



Seasoning and kiln-drying is so important a process in 
the manufacture of woods that a need is keenly felt fox 
fuller information regarding it, based upon scientific study 
of the behavior of various species at different mechanical 
temperatures and under different mechanical drying proc- 
esses. The special precautions necessary to prevent loss 
of strength or distortion of shape render the drying of 
wood especially difficult. 

All wood when undergoing a seasoning process, either 
natural (by air) or mechanical (by steam or heat in a dry 
kiln), checks or splits more or less. This is due to the 
uneven drying-out of the wood and the consequent strains 
exerted in opposite directions by the wood fibres in shrink- 
ing. This shrinkage, it has been proven, takes place both 
end- wise and across the grain of the wood. The old tradi- 
tion that wood does not shrink end-wise has long since 
been shattered, and it has long been demonstrated that 
there is an end-wise shrinkage. 

In some woods it is ver)j>-light, while in others it is easily 
perceptible. It is claimed that the average end shrink- 
age, taking all the woods, is only about 1| per cent. This, 
however, probably has relation to the average shrinkage 
on ordinary lumber as it is used and cut and dried. Now 
if we depart from this and take veneer, or basket stock, 
or even stave bolts where they are boiled, causing swelling 
both end-wise and across the grain or in dimension, after 
they are thoroughly dried, there is considerably more 
evidence of end shrinkage. In other words, a slack barrel 
stave of elm, say, 28 or 30 inches in length, after being 



boiled might shrink as much in thoroughly drying-out 
as compared to its length when freshly cut, as a 12-foot 
elm board. 

It is in cutting veneer that this end shrinkage becomes 
most readily apparent. In trimming with scoring knives 
it is done to exact measure, and where stock is cut to fit 
some specific place there has been observed a shrinkage 
on some of the softer woods, like cottonwood, amounting 
to fully I of an inch in 36 inches. And at times where 
drying has been thorough the writer has noted a shrinkage 
of I of an inch on an ordinary elm cabbage-crate strip 
36 inches long, sawed from the log without boiling. 

There are really no fixed rules of measurement or al- 
lowance, however, because the same piece of wood may 
vary under different conditions, and, again, the grain 
may cross a little or wind around the tree, and this of 
itself has a decided effect on the amount of what is termed 
"end shrinkage." 

There is more checking in the wood of the broad-leaf 
(hardwood) trees than in that of the coniferous (softwood) 
trees, more in sapwood than in heartwood, and more in 
summer-wood than in spring-wood. 

Inasmuch as under normal conditions of weather, water 
evaporates less rapidly during the early seasoning of 
winter, wood that is cut in the autumn and early winter 
is considered less subject to checking than that which is 
cut in spring and summer. 

Rapid seasoning, except after wood has been thoroughly 
soaked or steamed, almost invariably results in more or 
less serious checking. All hardwoods which check or 
warp badly during the seasoning should be reduced to 
the smallest practicable size before drying to avoid the 
injuries involved in this process, and wood once seasoned 
should never again be exposed to the weather, since all injuries 
due to seasoning are thereby aggravated. 

Seasoning increases the strength of wood in every re- 
spect, and it is therefore of great importance to protect 
the wood against moisture. 


Changes rendering Drying difficult 

An important property rendering drying of wood pe- 
culiarly difficult is the changes which occur in the hy- 
groscopic properties of the surface of a stick, and the rate 
at which it will allow moisture to pass through it. If 
wood is dried rapidly the surface soon reaches a condition 
where the transfusion is greatly hindered and sometimes 
appears almost to cease. The nature of this action is 
not well understood and it differs greatly in different species. 
Bald cypress ( Taxodium distichum) is an example in which 
this property is particularly troublesome. The difficulty 
can be overcome by regulating the humidity during the 
drying operation. It is one of the factors entering into 
production of what is called ''case-hardening" of wood, 
where the surface of the piece becomes hardened in a 
stretched or expanded condition, and subsequent shrink- 
age of the interior causes "honeycombing," "hollow- 
horning," or internal checking. The outer surface of 
the wood appears to undergo a chemical change in the 
nature of hydrolization or oxidization, which alters the 
rate of absorption and evaporation in the air. 

As the total amount of shrinkage varies with the rate 
at which the wood is dried, it follows that the outer sur- 
face of a rapidly dried board shrinks less than the interior. 
This sets up an internal stress, which, if the board be 
afterward resawed into two thinner boards by slicing it 
through the middle, causes the two halves to cup with 
their convex surfaces outward. This effect may occur 
even though the moisture distribution in the board has 
reached a uniform condition, and the board is thoroughly 
dry before it is resawed. It is distinct from the well- 
known "case-hardening" effect spoken of above, which 
is caused by unequal moisture conditions. 

The manner in which the water passes from the in- 
terior of a piece of wood to its surface has not as yet been 
fully determined, although it is one of the most important 
factors which influence drying. This must involve a 
transfusion of moisture through the cell walls, since, as 
already mentioned, except for the open vessels in the hard- 


woods, free resin ducts in the softwoods, and possibly the 
intercellular spaces, the cells of green wood are enclosed 
by membranes and the water must pass through the walls 
or the membranes of the pits. Heat appears to increase 
this transfusion, but experimental data are lacking. 

It is evident that to dry wood properly a great many 
factors must be taken into consideration aside from the 
mere evaporation of moisture. 

Losses Due to Improper Kiln-drying 

In some cases there is practically no loss in drying, but 
more often it ranges from 1 to 3 per cent, and 7 to 10 per 
cent in refractory woods such as gum. In exceptional 
instances the losses are as high as 33 per cent. 

In air-drying there is little or no control over the proc- 
ess; it may take place too rapidly on some days and too 
slowly on others, and it may be very non-uniform. 

Hardwoods in large sizes almost invariably check. 

By proper kiln-drying these unfavorable circumstances 
may be eliminated. However, air-drying is unquestion- 
ably to be preferred to bad kiln-drying, and when there 
is any doubt in the case it is generally safer to trust to 

If the fundamental principles are all taken care of, green 
lumber can be better dried in the dry kiln. 

Properties of Wood that affect Drying 

It is clear, from the previous discussion of the structure 
of wood, that this property is of first importance among 
those influencing the seasoning of wood. The free water 
may usually be extracted quite readily from porous hard- 
woods. The presence of tyloses in white oak makes even 
this a difficult problem. On the other hand, its more 
complex structure usually renders the hygroscopic mois- 
ture quite difficult to extract. 

The lack of an open, porous structure renders the trans- 
fusion of moisture through some woods very slow, while 
the reverse may be true of other species. The point of 
interest is that all the different variations in structure 


affect the drying rates of woods. The structure of the 
gums suggests relatively easy seasoning. 

Shrinkage is a very important factor affecting the dry- 
ing of woods. Generally speaking, the greater the shrink- 
age the more difficult it is to dry wood. Wood shrinks 
about twice as much tangentially as radially, thus intro- 
ducing very serious stresses which may cause loss in woods 
whose total shrinkage is large. It has been found that 
the amount of shrinkage depends, to some extent, on the 
rate and temperature at which woods season. Rapid 
drying at high or low temperature results in slight shrink- 
age, while slow drying, especially at high temperature, 
increases the shrinkage. 

As some woods must be dried in one way and others in 
other ways, to obtain the best general results, this effect 
may be for the best in one case and the reverse in others. 
As an example one might cite the case of Southern white 
oak. This species must be dried very slowly at low tem- 
peratures in order to avoid the many evils to which it is 
heir. It is interesting to note that this method tends to 
increase the shrinkage, so that one might logically ex- 
pect such treatment merely to aggravate the evils. Such 
is not the case, however, as too fast drying results in other 
defects much worse than that of excessive shrinkage. 

Thus we see that the shrinkage of any given species of 
wood depends to a great extent on the method of drying. 
Just how much the shrinkage of gum is affected by the 
temperature and drying rate is not known at present. 
There is no doubt that the method of seasoning affects 
the shrinkage of the gums, however. It is just possible 
that these woods may shrink longitudinally more than 
is normal, thus furnishing another cause for their peculiar 
action under certain circumstances. It has been found 
that the properties of wood which affect the seasoning of 
the gums are, in the order of their importance: (1) The 
indeterminate and erratic grain; (2) the uneven shrink- 
age with the resultant opposing stresses; (3) the plasticity 
under high temperature while moist; and (4) the slight 
apparent lack of cohesion between the fibres. The first, 
second, and fourth properties are clearly detrimental, 


while the third may possibly be an advantage in reducing 
checking and '^case-hardening." 

The grain of the wood is a prominent factor also af- 
fecting the problem. It is this factor, coupled with uneven 
shrinkage, which is probably responsible, to a large extent, 
for the action of the gums in drying. The grain may be 
said to be more or less indeterminate. It is usually spiral, 
and the spiral may reverse from year to year of the tree's 
growth. When a board in which this condition exists 
begins to shrink, the result is the development of opposing 
stresses, the effect of which is sometimes disastrous. The 
shrinkage around the knots seems to be particularly un- 
even, so that checking at the knots is quite common. 

Some woods, such as Western red cedar, redwood, and 
eucalyptus, become very plastic when hot and moist. 
The result of drying-out the free water at high tempera- 
ture may be to collapse the cells. The gums are known 
to be quite soft and plastic, if they are moist, at high 
temperature, but they do not collapse so far as we have 
been able to determine. 

The cells of certain species of wood appear to lack 
cohesion, especially at the junction between the annual 
rings. As a result, checks and ring shakes are very com- 
mon in Western larch and hemlock. The parenchyma 
cells of the medullary rays in oak do not cohere strongly 
and often check open, especially when steamed too severely. 

Unsolved Problems in Kiln-drying 

1. Physical data of the properties of wood in relation 
to heat are meagre. 

2. Figures on the specific heat of wood are not readily 
available, though upon this rests not only the ex- 
act operation of heating coils for kilns, but the 
theory of kiln-drying as a whole. 

3. Great divergence is shown in the results of experi- 
ments in the conductivity of wood. It remains 
to be seen whether the known variation of con- 
ductivity with moisture content will reduce these 
results to uniformity. 


4. The maximum or highest temperature to which 
the different species of wood may be exposed with- 
out serious loss of strength has not yet been deter- 

5. The optimum or absolute correct temperature for 
drying the different species of wood is as yet 
entirely unsettled. 

6. The inter-relation between wood and water is as 
imperfectly known to dry-kiln operators as that 
between wood and heat. 

7. What moisture conditions obtain in a stick of air- 
dried wood? 

8. How is the moisture distinguished? 

9. What is its form? 

10. What is the meaning of the peculiar surface con- 
ditions which even in air-dried wood appear to 
indicate incipient ' ' case-hardening ' ' ? 

11. The manner in which the water passes from the 
interior of a piece of wood to its surface has not 
as yet been fully determined. 

These questions can be answered thus far only by specu- 
lation or, at best, on the basis of incomplete data. 

Until these problems are solved, kiln-drying must 
necessarily remain without the guidance of complete 
scientific theory. 

A correct understanding of the principles of drying is 
rare, and opinions in regard to the subject are very diverse. 
The same lack of knowledge exists in regard to dry kilns. 
The physical properties of the wood which complicate 
the drying operation and render it distinct from that of 
merely evaporating free water from some substance like 
a piece of cloth must be studied experimentally. It can- 
not well be worked out theoretically. 



Methods of Drying 

The choice of a method of drying depends largely upon 
the object in view. The principal objects may be grouped 
under three main heads, as follows: 

1. To reduce shipping weight. 

2. To reduce the quantity necessary to carry in stock. 

3. To prepare the wood for its ultimate use and im- 

prove its qualities. 

When wood will stand the temperature without ex- 
cessive checking or undue shrinkage or loss in strength, 
the first object is most readily attained by heating the 
wood above the boiling point in a closed chamber, with 
a large circulation of air or vapor, so arranged that the 
excess steam produced will escape. This process mani- 
festly does not apply to many of the hardwoods, but is 
applicable to many of the softwoods. It is used especially 
in the northwestern part of the United States, where 
Douglas fir boards one inch thick are dried in from 40 to 
65 hours, and sometimes in as short a time as 24 hours. 
In the latter case superheated steam at 300 degrees Fah- 
renheit was forced into the chamber but, of course, the 
lumber could not be heated thereby much above the boil- 
ing point so long as it contained any free water. 

This lumber, however, contained but 34 per cent moist- 
ure to start with, and the most rapid rate was 1.6 per cent 
loss per hour. 

The heat of evaporation may be supplied either by 
superheated steam or by steam pipes within the kiln 

The quantity of wood it is necessary to carry in stock 


is naturally reduced when either of the other two objects 
is attained and, therefore, need not necessarily be dis- 

In drying to prepare for use and to improve quality, 
careful and scientific drying is called for. This applies 
more particularly to the hardwoods, although it may be 
required for softwoods also. 

Drying at Atmospheric Pressure 

Present practice of kiln-drying varies tremendously 
and there is no uniformity or standard method. 

Temperatures vary anywhere from 65 to 165 degrees 
Fahrenheit, or even higher, and inch boards three to six 
months on the sticks are being dried in from four days to 
three weeks, and three-inch material in from two to five 

All methods in use at atmospheric pressure may be 
classified under the following headings. The kilns may 
be either progressive or compartment, and preliminary 
steaming may or may not be used with any one of these 
methods : 

1. Dry air heated. This is generally obsolete. 

2. Moist air. 

a. Ventilated. 

b. Forced draft. 

c. Condensing. 

d. Humidity regulated. 

e. Boiling. 

3. Superheated steam. 

Drying under Pressure and Vacuum 

Various methods of drying wood under pressures other 
than atmospheric have been tried. Only a brief mention 
of this subject will be made. Where the apparatus is 
available probably the quickest way to dry wood is first 
to heat it in saturated steam at as high a temperature 
as the species can endure without serious chemical change 
until the heat has penetrated to the center, then follow 
this with a vacuum. 


By this means the self-contained specific heat of the 
wood and the water is made available for the evaporation, 
and the drying takes place from the inside outwardly, 
just the reverse of that which occurs by drying by means 
of external heat. 

When the specimen has cooled this process is then to be 
repeated until it has dried down to fibre-saturation point. 
It cannot be dried much below this point by this method, 
since the absorption during the heating operation will 
then equal the evaporation during the cooling. It may 
be carried further, however, by heating in partially hu- 
midified air, proportioning the relative humidity each 
time it is heated to the degree of moisture present in the 

The point to be considered in this operation is that 
during the heating process no evaporation shall be allowed 
to take place, but only during the cooling. In this way 
surface drying and "case-hardening" are prevented since 
the heat is from within and the moisture passes from the 
inside outwardly. However, with some species, notably 
oak, surface cracks appear as a network of fine checks 
along the medullary rays. 

In the first place, it should be borne in mind that it is 
the heat which produces evaporation and not the air nor 
any mysterious property assigned to a "vacuum." 

For every pound of water evaporated at ordinary tem- 
peratures approximately 1,000 British thermal units of 
heat are used up, or "become latent," as it is called. This 
is true whether the evaporation takes place in a vacuum 
or under a moderate air pressure. If this heat is not sup- 
plied from an outside source it must be supplied by the 
water itself (or the material being dried), the temperature 
of which will consequently fall until the surrounding 
space becomes saturated with vapor at a pressure cor- 
responding to the temperature which the water has reached; 
evaporation will then cease. The pressure of the vapor 
in a space saturated with water vapor increases rapidly 
with increase of temperature. At a so-called vacuum of 
28 inches, which is about the limit in commercial opera- 
tions, and in reality signifies an actual pressure of 2 inches 


of mercury column, the space will be saturated with vapor 
at 101 degrees Fahrenheit. Consequently, no evapora- 
tion will take place in such a vacuum unless the water be 
warmer than 101 degrees Fahrenheit, provided there is 
no air leakage. The qualification in regard to air is nec- 
essary, for the sake of exactness, for the following reason: 
In any given space the total actual pressure is made up 
of the combined pressures of all the gases present. If the 
total pressure ("vacuum") is 2 inches, and there is no air 
present, it is all produced by the water vapor (which 
saturates the space at 101 degrees Fahrenheit) ; but if 
some air is present and the total pressure is still maintained 
at 2 inches, then there must be less vapor present, since 
the air is producing part of the pressure and the space is 
no longer saturated at the given temperature. Conse- 
quently further evaporation may occur, with a correspond- 
ing lowering of the temperature of the water, until a balance 
is again reached. Without further explanation it is easy 
to see that but little water can be evaporated by a vacuum 
alone without addition of heat, and that the prevalent 
idea that a vacuum can of itself produce evaporation is 
a fallacy. If heat be supplied to the water, however, 
either by conduction or radiation, evaporation will take 
place in direct proportion to the amount of heat supplied, 
so long as the pressure is kept down by the vacuum 

At 30 inches of mercury pressure (one atmosphere) the 
space becomes saturated with vapor and equilibrium is 
established at 212 degrees Fahrenheit. If heat be now 
supplied to the water, however, evaporation will take 
place in proportion to the amount of heat supplied, so 
long as the pressure remains that of one atmosphere, just 
as in the case of the vacuum. Evaporation in this con- 
dition, where the vapor pressure at the temperature of 
the water is equal to the gas pressure on the water, 
is commonly called "boiling," and the saturated vapor 
entirely displaces the air under continuous operation. 
Whenever the space is not saturated with vapor, whether 
air is present or not, evaporation will take place, by boil- 
ing if no air be present or by diffusion under the presence 


of air, until an equilibrium between temperature and 
vapor pressure is resumed. 

Relative humidity is simply the ratio of the actual vapor 
pressure present in a given space to the vapor pressure 
when the space is saturated with vapor at the given tem- 
perature. It matters not whether air be present or not. 
One hundred per cent humidity means that the space 
contains all the vapor which it can hold at the given 
temperature — it is saturated. Thus at 100 per cent 
humidity and 212 degrees Fahrenheit the space is satu- 
rated, and since the pressure of saturated vapor at this 
temperature is one atmosphere, no air can be present 
under these conditions. If, however, the total pressure 
at this temperature were 20 pounds (5 pounds gauge), 
then it would mean that there was 5 pounds air pressure 
present in addition to the vapor, yet the space would still 
be saturated at the given temperature. Again, if the 
temperature were 101 degrees Fahrenheit, the pressure 
of saturated vapor would be only 1 pound, and the ad- 
ditional pressure of 14 pounds, if the total pressure were 
atmospheric, would be made up of air. In order to have 
no air present and the space still saturated at 101 degrees 
Fahrenheit, the total pressure must be reduced to 1 pound 
by a vacuum pump. Fifty per cent relative humidity, 
therefore, signifies that only half the amount of vapor 
required to saturate the space at the given temperature 
is present. Thus at 212 degrees Fahrenheit temperature 
the vapor pressure would only be 7| pounds (vacuum of 
15 inches gauge). If the total pressure were atmospheric, 
then the additional 7^ pounds would be simply air. 

"Live steam" is simply water-saturated vapor at a 
pressure usually above atmospheric. We may just as 
truly have live steam at pressures less than atmospheric, 
at a vacuum of 28 inches for instance. Only in the latter 
case its temperature would be lower, viz., 101 degrees 

Superheated steam is nothing more than water vapor 
at a relative humidity less than saturation, but is usually 
considered at pressures above atmospheric, and in the 
absence of air. The atmosphere at, say, 50 per cent rela- 


tive humidity really contains superheated steam or vapor, 
the only difference being that it is at a lower temperature 
and pressure than we are accustomed to think of in speak- 
ing of superheated steam, and it has air mixed with it to 
make up the deficiency in pressure below the atmosphere. 
Two things should now be clear; that evaporation is 
produced by heat and that the presence or absence of air 
does not influence the amount of evaporation. It does, 
however, influence the rate of evaporation, which is re- 
tarded by the presence of air. The main things influenc- 
ing evaporation are, first, the quantity of heat supplied 
and, second, the relative humidity of the immediately 
surrounding space. 

Drying by Superheated Steam 

What this term really signifies is simply water vapor 
in the absence of air in a condition of less than saturation. 
Kilns of this type are, properly speaking, vapor kilns, 
and usually operate at atmospheric pressure, but may be 
used at greater pressures or at less pressures. As stated 
before, the vapor present in the air at any humidity less 
than saturation is really "superheated steam," only at a 
lower pressure than is ordinarily understood by this term, 
and mixed with air. The main argument in favor of this 
process seems to be based on the idea that steam is moist 
heat. This is true, however, only when the steam is near 
saturation. When it is superheated it is just as dry as 
air containing the same relative humidity. For instance, 
steam at atmospheric pressure and heated to 248 degrees 
Fahrenheit has a relative humidity of only 50 per cent and 
is just as dry as air containing the same humidity. If 
heated to 306 degrees Fahrenheit, its relative humidity 
is reduced to 20 per cent; that is to say, the ratio of its 
actual vapor pressure (one atmosphere) to the pressure 
of saturated vapor at this temperature (five atmospheres) 
is 1:5, or 20 per cent. Superheated vapor in the absence 
of air, however, parts with its heat with great rapidity 
and finally becomes saturated when it has lost all of its 
ability to cause evaporation. In this respect it is more 
moist than air when it comes in contact with bodies which 


are at a lower temperature. When saturated steam is 
used to heat the lumber it can raise the temperature of 
the latter to its own temperature, but cannot produce 
evaporation unless, indeed, the pressure is varied. Only 
by the heat supplied above the temperature of saturation 
can evaporation be produced. 

Impregnation Methods 

Methods of partially overcoming the shrinkage by im- 
pregnation of the cell walls with organic materials closely 
allied to the wood substance itself are in use. In one of 
these which has been patented, sugar is used as the im- 
pregnating material, which is subsequently hardened or 
" caramelized" by heating. Experiments which the United 
States Forest Service has made substantiate the claims 
that the sugar does greatly reduce the shrinkage of the 
wood; but the use of impregnation processes is determined 
rather from a financial economic standpoint than by the 
physical result obtained. 

Another process consists in passing a current of elec- 
tricity through the wet boards or through the green logs 
before sawing. It is said that the ligno cellulose and the 
sap are thus transformed by electrolysis, and that the 
wood subsequently dries more rapidly. 

Preliminary Treatments 

In many dry kiln operations, especially where the kilns 
are not designed for treatments with very moist air, the 
wood is allowed to air-season from several months to a 
year or more before running it into the dry kiln. In this 
way the surface dries below its fibre-saturation point and 
becomes hardened or "set" and the subsequent shrink- 
age is not so great. Moreover, there is less danger of 
surface checking in the kiln, since the surface has already 
passed the danger point. Many woods, however, check 
severely in air-drying or case-harden in the air. It is 
thought that such woods can be satisfactorily handled in 
a humidity-regulated kiln direct from the saw. 

Preliminary steaming is frequently used to moisten the 
surface if case-hardened, and to heat the lumber through 


to the center before drying begins. This is sometimes 
done in a separate chamber, but more often in a com- 
partment of the kiln itself, partitioned off by means of a 
curtain which can be raised or lowered as circumstances 
require. This steaming is usually conducted at atmos- 
pheric pressure and frequently condensed steam is used 
at temperatures far below 212 degrees Fahrenheit. In 
a humidity-regulated kiln this preliminary treatment may 
be omitted, since nearly saturated conditions can be 
maintained and graduated as the drying progresses. 

Recently the process of steaming at pressures up to 
20 pounds gauge in a cylinder for short periods of time, 
varying from 5 to 20 minutes, is being advocated in the 
United States. The truck load is run into the cylinder, 
steamed, and then taken directly out into the air. It 
may subsequently be placed in the dry kiln if further dry- 
ing is desired. The self-contained heat of the wood evapo- 
rates considerable moisture, and the sudden drying of 
the boards causes the shrinkage to be reduced slightly 
in some cases. Such short periods of steaming under 
20 pounds pressure do not appear to injure the wood 
mechanically, although they do darken the color appreci- 
ably, especially of the sapwood of the species having a 
light-colored sap, as black walnut {Juglans nigra) and 
red gum {Liquidamher styraciflua). Longer periods of 
steaming have been found to weaken the wood. There 
is a great difference in the effect on different species, 

Soaking wood for a long time before drying has been 
practised, but experiments indicate that no particularly 
beneficial results, from the drying standpoint, are attained 
thereby. In fact, in some species containing sugars and 
allied substances it is probably detrimental from the 
shrinkage standpoint. If soaked in boiling water some 
species shrink and warp more than if dried without this 

In general, it may be said that, except possibly for 
short-period steaming as described above, steaming and 
soaking hardwoods at temperatures of 212 degrees Fahren- 
heit or over should be avoided if possible. 


It is the old saying that wood put into water shortly 
after it is felled, and left in water for a year or more, will 
be perfectly seasoned after a short subsequent exposure 
to the air. For this reason rivermen maintain that 
timber is made better by rafting. Herzenstein says: 
"Floating the timber down rivers helps to wash out the 
sap, and hence must be considered as favorable to its 
preservation, the more so as it enables it to absorb more 

Wood which has been buried in swamps is eagerly 
sought after by carpenters and joiners, because it has 
lost all tendency to warp and twist. When first taken 
from the swamp the long-immersed logs are very much 
heavier than water, but they dry with great rapidity. 
A cypress log from the Mississippi Delta, which two men 
could barely handle at the time it was taken out some 
years ago, has dried out so much since then that to-day 
one man can lift it with ease. White cedar telegraph 
poles are said to remain floating in the water of the Great 
Lakes sometimes for several years before they are set in 
lines and to last better than freshly cut poles. 

It is very probable that immersion for long periods in 
water does materially hasten subsequent seasoning. The 
tannins, resins, albuminous materials, etc., which are 
deposited in the cell walls of the fibres of green wood, and 
which prevent rapid evaporation of the water, undergo 
changes when under water, probably due to the action of 
bacteria which live without air, and in the course of time 
many of these substances are leached out of the wood. 
The cells thereby become more and more permeable to 
water, and when the wood is finally brought into the air 
the water escapes very rapidly and very evenly. Her- 
zenstein's statement that wood prepared by immersion 
and subsequent drying will absorb more preservative, 
and that with greater rapidity, is certainly borne out by 
experience in the United States. 

It is sometimes claimed that all seasoning preparatory 
to treatment with a substance like tar oil might be done 
away with by putting the green wood into a cylinder with 
the oil and heating to 225 degrees Fahrenheit, thus driving 


the water off in the form of steam, after which the tar oil 
would readily penetrate into the wood. This is the basis 
of the so-called ''Curtiss process" of timber treatment. 
Without going into any discussion of this method of 
creosoting, it may be said that the same objection made 
for steaming holds here. In order to get a temperature of 
212 degrees Fahrenheit in the center of the treated wood, 
the outside temperature would have to be raised so high 
that the strength of the wood might be seriously injured. 
A company on the Pacific coast which treats red fir piling 
asserts that it avoids this danger by leaving the green 
timber in the tar oil at a temperature which never exceeds 
225 degrees Fahrenheit for from five to twelve hours, until 
there is no further evidence of water vapor coming out of 
the wood. The tar oil is then run out, and a vacuum is 
created for about an hour, after which the oil is run in 
again and is kept in the cylinders under 100 pounds pres- 
sure for from ten to twelve hours, until the required amount 
of absorption has been reached (about 12 pounds per 
cubic foot). 

Out-of-door Seasoning 

The most effective seasoning is without doubt that 
obtained by the uniform, slow drying which takes place 
in properly constructed piles outdoors, under exposure 
to the winds and the sun. Lumber has always been 
seasoned in this way, which is still the best for ordinary 

It is probable for the sake of economy, air-drying will 
be eliminated in the drying process of the future without 
loss to the quality of the product, but as yet no effective 
method has been discovered whereby this may be ac- 
complished, because nature performs certain functions 
in air-drying that cannot be duplicated by artificial means. 
Because of this, hardwoods, as a rule, cannot be success- 
fully kiln-dried green or direct from the saw, and must 
receive a certain amount of preliminary air-drying before 
being placed in a dry kiln. 

The present methods of air-seasoning in use have been 
determined by long experience, and are probably as good 


as they could be made for present conditions. But the 
same care has not up to this time been given to the season- 
ing of such timber as ties, bridge material, posts, telegraph 
and telephone poles, etc. These have sometimes been 
piled more or less intelligently, but in the majority of 
cases their value has been too low to make it seem worth 
while to pile with reference to anything beyond con- 
venience in handling. 

In piling material for air-seasoning, one should utilize 
high, dry ground when possible, and see that the founda- 
tions are high enough off the ground, so that there is 
proper air circulation through the bottom of the piles, 
and also that the piles are far enough apart so that the 
air may circulate freely through and around them. 

It is air circulation that is desired in all cases of drying, 
both in dry kilns and out-of-doors, and not sunshine; that 
is, not the sun shining directly upon the material. The 
ends also should be protected from the sun, and every- 
thing possible done to induce a free circulation of air, and 
to keep the foundations free from all plant growth. 

Naturally, the heavier the material to be dried, the more 
difficulty is experienced from checking, which has its most 
active time in the spring when the sap is rising. In fact 
the main period of danger in material checking comes 
with the March winds and the April showers, and not 
infrequently in the South it occurs earlier than that. In 
other words, as soon as the sap begins to rise, the timber 
shows signs of checking, and that is the time to take extra 
precautions by careful piling and protection from the sun. 
When the hot days of summer arrive the tendency to 
check is not so bad, but stock will sour from the heat, 
stain from the sap, mildew from moisture, and fall a prey 
to wood-destroying insects. 

It has been proven in a general way that wood will 
season more slowly in winter than in summer, and also 
that the water content during various months varies. In 
the spring the drying-out of wood cut in October and 
November will take place more rapidly. 



Advantages of Kiln-drying over Air-drying 

Some of the advantages of kiln-drying to be secured 
over air-drying in addition to reducing the shipping weight 
and lessening quantity of stock are the following: 

1. Less material lost. 

2. Better quality of product. 

3. Prevention of sap stain and mould. 

4. Fixation of gums and resins. 

5. Reduction of hygroscopicity. 

This reduction in the tendency to take up moisture 
means a reduction in the "working" of the material which, 
even though slight, is of importance. 

The problem of drying wood in the best manner divides 
itself into two distinct parts, one of which is entirely con- 
cerned with the behavior of the wood itself and the physi- 
cal phenomena involved, while the other part has to do 
with the control of the drying process. 

Physical Conditions governing the Drying of Wood 

1. Wood is soft and plastic while hot and moist, and 

becomes "set" in whatever shape it dries. Some 
species are much more plastic than others. 

2. Wood substance begins to shrink only when it dries 

below the fibre-saturation point, at which it con- 
tains from 25 to 30 per cent moisture based on 
its dry weight. Eucalyptus and certain other species 
appear to be exceptions to this law. 

3. The shrinkage of wood is about twice as great cir- 

cumferentially as in the radial direction; length- 
wise, it is very slight. 

4. Wood shrinks most when subjected, while kept 

moist, to slow drying at high temperatures. 


5. Rapid drying produces less shrinkage than slow dry- 

ing at high temperatures, but is apt to cause case- 
hardening and honeycombing, especially in dense 

6. Case-hardening, honeycombing, and cupping result 

directly from conditions 1, 4, and 5, and chemical 
changes of the outer surface. 

7. Brittleness is caused by carrying the drying process 

too far, or by using too high temperatures. Safe 
limits of treatment vary greatly for different species. 

8. Wood absorbs or loses moisture in proportion to the 

relative humidity in the air, not according to the 
temperature. This property is called its ''hygro- 

9. Hygroscopicity and ''working" are reduced but 

not eliminated by thorough drying. 

10. Moisture tends to transfuse from the hot towards 
the cold portion of the wood. 

11. Collapse of the cells may occur in some species 
while the wood is hot and plastic. This collapse 
is independent of subsequent shrinkage. 

Theory of Kiln-drying 

The dry kiln has long since acquired particular ap- 
preciation at the hands of those who have witnessed its 
time-saving qualities, when practically applied to the dry- 
ing of timber. The science of drying is itself of the simplest, 
the exposure to the air being, indeed, the only means 
needed where the matter of time is not called into question. 
Otherwise, where hours, even minutes, have a marked 
significance, then other means must be introduced to 
bring about the desired effect. In any event, however, 
the same simple and natural remedy pertains, — ■ the 
absorption of moisture. This moisture in green timber 
is known as "sap", which is itself composed of a number 
of ingredients, most important among which are water, 
resin, and albumen. 

All dry kilns in existence use heat to season timber; 


that is, to drive out that portion of the "sap" which is 

The heat does not drive out the resin of the pines nor 
the albumen of the hardwoods. It is really of no ad- 
vantage in this respect. Resin in its hardened state as 
produced by heat is only slowly soluble in water and 
contains a large proportion of carbon, the most stable 
form of matter. Therefore, its retention in the pores of 
the wood is a positive advantage. 

To produce the ideal effect the drying must commence 
at the heart of the piece and work outward, the moisture 
being removed from the surface as fast as it exudes from 
the pores of the wood. To successfully accomplish this, 
adjustments must be available to regulate the tempera- 
ture, circulation, and humidity according to the varia- 
tions of the atmospheric conditions, the kind and condition 
of the material to be dried. 

This ideal effect is only attained by the use of a type 
of dry kiln in which the surface of the lumber is kept soft, 
the pores being left open until all the moisture within has 
been volatilized by the heat and carried off by a free circu- 
lation of air. When the moisture has been removed from 
the pores, the surface is dried without closing the pores, 
resulting in timber that is clean, soft, bright, straight, and 
absolutely free from stains, checks, or other imperfections. 

Now, no matter how the method of drying may be 
applied, it must be remembered that vapor exists in the 
atmosphere at all times, its volume being regulated by 
the capacity of the temperature absorbed. To kiln-dry 
properly, a free current of air must be maintained, of 
sufficient volume to carry off this moisture. Now, the 
capacity of this air for drying depends entirely upon the 
ability of its temperature to absorb or carry off a larger 
proportion of moisture than that apportioned by natural 
means. Thus, it will be seen, a cubic foot of air at 32 
degrees Fahrenheit is capable of absorbing only two grains 
of water, while at 160 degrees, it will dispose of ninety 
grains. The air, therefore, should be made as dry as 
possible and caused to move freely, so as to remove all 
moisture from the surface of the wood as soon as it appears. 


Thus the heat effects a double purpose, not only increas- 
ing the rate of evaporation, but also the capacity of the 
air for absorption. Where these means are applied, which 
rely on the heat alone to accomplish this purpose, only that 
of the moisture which is volatile succumbs, while the al- 
bumen and resin becoming hardened under the treatment 
close up the pores of the wood. This latter result is 
oft-times accomplished while moisture yet remains and 
which in an enforced effort to escape bursts open the cells 
in which it has been confined and creates what is known 
as "checks." 

Therefore, taking the above facts into consideration, 
the essentials for the successful kiln-drying of wood may 
be enumerated as follows: 

1. The evaporation from the surface of a stick should 

not exceed the rate at which the moisture trans- 
fuses from the interior to the surface. 

2. Drying should proceed uniformly at all points, 

otherwise extra stresses are set up in the wood, 
causing warping, etc. 

3. Heat should penetrate to the interior of the piece 

before drying begins. 

4. The humidity should be suited to the condition 

of the wood at the start and reduced in the proper 
ratio as drying progresses. With wet or green 
wood it should usually be held uniform at a degree 
which will prevent the surface from drying below 
its saturation point until all the free water has 
evaporated, then gradually reduced to remove the 
hygroscopic moisture. 

5. The temperature should be uniform and as high 

as the species under treatment will stand without 
excessive shrinkage, collapse, or checking. 

6. Rate of drying should be controlled by the amount 

of humidity in the air and not by the rate of circu- 
lation, which should be made ample at all times. 

7. In drying refractory hardwoods, such as oak, best 

results are obtained at a comparatively low tempera- 


ture. In more easily dried hardwoods, such as 
maple, and some of the more difficult softwoods, 
as cypress, the process may be hastened hj a higher 
temperature but not above the boiling point. In 
many of the softwoods, the rate of drying may be 
very greatly increased by heating above the boil- 
ing point with a large circulation of vapor at at- 
mospheric pressure. 

8. Unequal shrinkage between the exterior and in- 

terior portions of the wood and also unequal chemical 
changes must be guarded against by temperatures 
and humidities suited to the species in question 
to prevent subsequent cupping and warping. 

9. The degree of dryness attained should conform 

to the use to which the wood is put. 
10. Proper piling of the material and weighting to pre- 
vent warping are of great importance. 

Requirements in a Satisfactory Dry Kiln 

The requirements in a satisfactory dry kiln are: 

1. Control of humidity at all times. 

2. Ample air circulation at all points. 

3. Uniform and proper temperatures. 

In order to meet these requirements the United States 
Forestry Service has designed a kiln in which the humidity, 
temperature, and circulation can be controlled at all times. 

Briefly, it consists of a drying chamber with a partition 
on either side, making two narrow side chambers open 
top and bottom. 

The steam pipes are in the usual position underneath 
the material to be dried. 

At the top of the side chambers is a spray; at the bottom 
are gutters and an eliminator or set of baffle plates to 
separate the fine mist from the air. 

The spray accomplishes two things: It induces an in- 
creased circulation and it regulates the humidity. This is 
done by regulating the temperature of the spray water. 

The air under the heating coil is saturated at whatever 



temperature is required. This temperature is the dew 
point of the air after it passes up into the drying chamber 
above the coils. Knowing the temperature in the drying 
room and the dew point, the relative humidity is thus 

The relative humidity is simply the ratio of the vapor 
pressure at the dew point to the pressure of saturated 
vapor (see Fig. 30). 


Fig. 30. Section through United States Forestry Service Humidity- 
controlled Dry Kiln. 

Theory and Description of the Forestry Service Kiln 

The humidities and temperatures in the piles of lumber 
are largely dependent upon the circulation of air within 
the kiln. The temperature and humidity within the kiln, 
taken alone, are no criterion of the conditions of drying 
within the pile of lumber if the circulation in any portion 


is deficient. It is possible to have an extremely rapid cir- 
culation of air within the dry kiln itself and yet have 
stagnation within the individual piles, the air passing 
chiefly through open spaces and channels. Wherever 
stagnation exists or the movement of air is too sluggish 
the temperature will drop and the humidity increase, 
perhaps to the point of saturation. 

When in large kilns the forced circulation is in the op- 
posite direction from that induced by the cooling of the 
air by the lumber, there is always more or less uncertainty 
as to the movement of the air through the piles. Even 
with the boards placed edge-wise, with stickers running 
vertically, and with the heating pipes beneath the lumber, 
it was found that although the air passed upward through 
most of the spaces it was actually descending through 
others, so that very unequal drying resulted. While 
edge piling would at first thought seem ideal for the freest 
circulation in an ordinary kiln with steam pipes below, it 
in fact produces an indeterminate condition; air columns 
may pass downward through some channels as well as up- 
ward through others, and probably stagnate in still others. 
Nevertheless, edge piling is greatly superior to flat piling 
where the heating system is below the lumber. 

From experiments and from study of conditions in 
commercial kilns the idea was developed of so arranging 
the parts of the kiln and the pile of lumber that advantage 
might be taken of this cooling of the air to assist the circu- 
lation. That this can be readily accomplished without 
doing away with the present features of regulation of 
humidity by means of a spray of water is clear from Fig. 
30, which shows a cross-section of the improved humidity- 
regulated dry kiln. 

In the form shown in the sketch a chamber or flue B 
runs through the center near the bottom. This flue is 
only about 6 or 7 feet in height and, together with the 
water spray F and the baffle plates DD, constitutes the 
humidity-control feature of the kiln. This control of 
humidity is affected by the temperature of the water 
used in the spray. This spray completely saturates the 
air in the flue B at whatever predetermined temperature 


is required. The baffle plates DD are to separate all 
entrained particles of water from the air, so that it is de- 
livered to the heaters in a saturated condition at the re- 
quired temperature. This temperature is, therefore, the 
dew point of the air when heated above, and the method 
of humidity control may therefore be called the dew-point 
method. It is a very simple matter by means of the hu- 
midity diagram (see Fig. 93), or by a hydrodeik (Fig. 94), 
to determine what dew-point temperature is needed for 
any desired humidity above the heaters. 

Besides regulating the humidity the spray F also acts as 
an ejector and forces circulation of air through the flue B. 
The heating system H is concentrated near the outer- (i^^^'*'^-^^^'*-' 
walls, so as to heat the rising column of air. The tempera- (^^^j^^^tr^ 
ture within the drying chamber is controlled by means J^ '"^ 

of any suitable thermostat, actuating a valve on the main 
steam line. The lumber is piled in such a way that the 
stickers slope downward toward the sides of the kiln. 

M is an auxiliary steam spray pointing downward for 
use at very high temperatures. C is a gutter to catch 
the precipitation and conduct it back to the pump, the 
water being recirculated through the sprays. G is a pipe 
condenser for use toward the end of the drying operation. 
K is a baffle plate for diverting the heated air and at the 
same time shielding the under layers of boards from direct 
radiation of the steam pipes. 

The operation of the kiln is simple. The heated air 
rises above the pipes HH and between the piles of lumber. 
As it comes in contact with the piles, portions of it are 
cooled and pass downward and outward through the layers 
of boards into the space between the condensers GG. 
Here the column of cooled air descends into the spray flue 
B, where its velocity is increased by the force of the water 
spray. It then passes out from the baffle plates to the 
heaters and repeats the cycle. 

One of the greatest advantages of this natural circula- 
tion method is that the colder the lumber when placed in 
the kiln the greater is the movement produced, under the 
very conditions which call for the greatest circulation — 
just the opposite of the direct-circulation method. This 


is a feature of the greatest importance in winter, when the 
lumber is put into the kiln in a frozen condition. One 
truckload of lumber at 60 per cent moisture may easily 
contain over 7,000 pounds of ice. 

In the matter of circulation the kiln is, in fact, seldom 
regulatory — the colder the lumber the greater the circu- 
lation produced, with the effect increased toward the cooler 
and wetter portions of the pile. 

Preliminary steaming may be used in connection with 
this kiln, but experiments indicate that ordinarily it is 
not desirable, since the high humidity which can be secured 
gives as good results, and being at as low a temperature 
as desired, much better results in the case of certain dif- 
ficult woods like oak, eucalyptus, etc., are obtained. 

This kiln has another advantage in that its operation 
is entirely independent of outdoor atmospheric conditions, 
except that barometric pressure will effect it slightly. 



Drying is an essential part of the preparation of wood 
for manufacture. For a long time the only drying process 
used or known was air-drying, or the exposure of wood to 
the gradual drying influences of the open air, and is what 
has now been termed ''preliminary seasoning." This 
method is without doubt the most successful and effective 
seasoning, because nature performs certain functions in 
air-drying that cannot be duplicated by artificial means. 
Because of this, hardwoods, as a rule, cannot be success- 
fully kiln-dried green or direct from the saw. 

Within recent years, considerable interest is awaken- 
ing among wood users in the operation of kiln-drying. 
The losses occasioned in air-drying and in improper kiln- 
drying, and the necessity for getting material dry as 
quickly as possible from the saw, for shipping purposes 
and also for manufacturing, are bringing about a realiza- 
tion of the importance of a technical knowledge of the 


The losses which occur in air-drying wood, through 
checking, warping, staining, and rotting, are often greater 
than one would suppose. While correct statistics of this 
nature are difficult to obtain, some idea may be had of 
the amount of degrading of the better class of lumber. 
In the case of one species of soft wood, Western larch, it 
is commonly admitted that the best grades fall off sixty 
to seventy per cent in air-drying, and it is probable that 
the same is true in the case of Southern swamp oaks. In 
Western yellow pine, the loss is great, and in the Southern 
red gum, it is probably as much as thirty per cent. It 
may be said that in all species there is some loss in air- 
drying, but in some easily dried species such as spruce, 
hemlock, maple, etc., it is not so great. 

It would hardly be correct to state at the present time 
that this loss could be entirely prevented by proper methods 
of kiln-drying the green lumber, but it is safe to say that 
it can be greatly reduced. 

It is well where stock is kiln-dried direct from the saw 
or knife, after having first been steamed or boiled — as 
in the case of veneers, etc., — to get them into the kiln 
while they are still warm, as they are then in good con- 
dition for kiln-drying, as the fibres of the wood are soft 
and the pores well opened, which will allow of forcing 
the evaporation of moisture without much damage being 
done to the material. 

With softwoods it is a common practice to kiln-dry 
direct from the saw. This procedure, however, is ill 
adapted for the hardwoods, in which it would produce 
such warping and checking as would greatly reduce the 
value of the product. Therefore, hardwoods, as a rule, 
are more or less thoroughly air-dried before being placed 
in the dry kiln, where the residue of moisture may be 
reduced to within three or four per cent, which is much 
lower than is possible by air-drying only. 

It is probable that for the sake of economy, air-drying 
will be eliminated in the drying processes of the future with- 
out loss to the quality of the product, but as yet no method 
has been discovered whereby this may be accomplished. 

The dry kiln has been, and probably still is, one of the 


most troublesome factors arising from the development 
of the timber industry. In the earlier days, before power 
machinery for the working-up of timber products came 
into general use, dry kilns were unheard-of, air-drying 
or seasoning was then relied upon solely to furnish the 
craftsman with dry stock from which to manufacture his 
product. Even after machinery had made rapid and 
startling strides on its way to perfection, the dry kiln re- 
raiained practically an unknown quantity, but gradually, 
as the industry developed and demand for dry material 
increased, the necessity for some more rapid and positive 
method of seasoning became apparent, and the subject of 
artificial drying began to receive the serious attention of 
the more progressive and energetic members of the craft. 

Kiln-drying which is an artificial method, originated 
in the effort to improve or shorten the process, by sub- 
jecting the wood to a high temperature or to a draught of 
heated air in a confined space or kiln. In so doing, time 
is saved and a certain degree of control over the drying 
operation is secured. 

The first efforts in the way of artificial drying were con- 
fined to aiding or hastening nature in the seasoning process 
by exposing the material to the direct heat from fires built 
in pits, over which the lumber was piled in a way to ex- 
pose it to the heat rays of the fires below. This, of course, 
was a primitive, hazardous, and very unsatisfactory 
method, to say the least, but it marked the first step in 
the evolution of the present-day dry kiln, and in that 
particular only is it deserving of mention. 

Underlying Principles 

In addition to marking the first step in artificial drying, 
it illustrated also, in the simplest manner possible, the 
three underlying principles governing all drying problems: 
(1) The application of heat to evaporate or volatilize the 
water contained in the material; (2) with sufficient air 
in circulation to carry away in suspension the vapor thus 
liberated; and (3) with a certain amount of humidity 
present to prevent the surface from drying too rapidly 
while the heat is allowed to penetrate to the interior. The 


last performs two distinct functions: (a) It makes the 
wood more permeable to the passage of the moisture 
from the interior of the wood to the surface, and (b) it 
supphes the latent heat necessary to evaporate the mois- 
ture after it reaches the surface. The air circulation 
is important in removing the moisture after it has 
been evaporated by the heat, and ventilation also 
serves the purpose of bringing the heat in contact with 
the wood. If, however, plain, dry heat is applied to the 
wood, the surface will become entirely dry before the in- 
terior moisture is even heated, let alone removed. This 
condition causes "case-hardening" or "hollow-horning." 
So it is very essential that sufficient humidity be main- 
tained to prevent the surface from drying too rapidly, 
while the heat is allowed to penetrate to the interior. 

This humidity or moisture is originated by the evapora- 
tion from the drying wood, or by the admission of steam 
into the dry kiln by the use of steam spray pipes, and is 
absolutely necessary in the process of hastening the dry- 
ing of wood. With green lumber it keeps the sap near 
the surface of the piece in a condition that allows the 
escape of the moisture from its interior; or, in other words, 
it prevents the outside from drying first, which would 
close the pores and cause case-hardening. 

The great amount of latent heat necessary to evaporate 
the water after it has reached the surface is shown by the 
fact that the evaporation of only one pound of water will 
extract approximately 66 degrees from 1,000 cubic feet 
of air, allowing the air to drop in temperature from 154 to 
84 degrees Fahrenheit. In addition to this amount of heat, 
the wood and the water must also be raised to the tempera- 
ture at which the drying is to be accompUshed. 

It matters not what type of dry kiln is used, source or 
application of heating medium, these underlying principles 
remain the same, and must be the first things considered 
in the design or selection of the equipment necessary for 
producing the three essentials of drying: Heat, humidity, 
and circulation. 

Although these principles constitute the basis of all 
drying problems and must, therefore, be continually 


carried in mind in the consideration of them, it is equally 
necessary to have a comprehensive understanding of the 
characteristics of the materials to be dried, and its action 
during the drying process. All failures in the past, in 
the drying of timber products, can be directly attributed 
to either the kiln designer's neglect of these things, or his 
failure to carry them fully in mind in the consideration 
of his problems. 

Wood has characteristics very much different from those 
of other materials, and what little knowledge we have 
of it and its properties has been taken from the accumu- 
lated records of experience. The reason for this imperfect 
knowledge lies in the fact that wood is not a homogeneous 
material like the metals, but a complicated structure, and 
so variable that one stick will behave in a manner widely 
different from that of another, although it may have been 
cut from the same tree. 

The great variety of woods often makes the mere dis- 
tinction of the kind or species of the tree most difficult. 
It is not uncommon to find men of long experience dis- 
agree as to the kind of tree a certain piece of lumber was 
cut from, and, in some cases, there is even a wide dif- 
ference in the appearance and evidently the structure of 
timber cut from the same tree. 

Objects of Kiln-drying 

The objects of kiln-drying wood may be placed under 
three main headings: (1) To reduce shipping expenses; 
(2) to reduce the quantity necessary to maintain in stock; 
and (3) to reduce losses in air-drying and to properly 
prepare the wood for subsequent use. Item number 2 
naturally follows as a consequence of either 1 or 3. The 
reduction in weight on account of shipping expenses is 
of greatest significance with the Northwestern lumbermen 
in the case of Douglas fir, redwood. Western red cedar, 
sugar pine, bull pine, and other softwoods. 

Very rapid methods of rough drying are possible with 
some of these species, and are in use. High temperatures 
are used, and the water is sometimes boiled off from the 
wood by heating above 212 degrees Fahrenheit. These 


high-temperature methods will not apply to the majority 
of hardwoods, however, nor to many of the softwoods. 

It must first of all be recognized that the drying of 
lumber is a totally different operation from the drying 
of a fabric or of thin material. In the latter, it is largely 
a matter of evaporated moisture, but wood is not only 
hygroscopic and attracts moisture from the air, but its 
physical behavior is very complex and renders the ex- 
traction of moisture a very comphcated process. 

An idea of its complexity may be had by mentioning some 
of the conditions which must be contended with. Shrink- 
age is, perhaps, the most important. This is unequal 
in different directions, being twice as great tangentially 
as radially and fifty times as great radially as longitudi- 
nally. Moreover, shrinkage is often unequal in different 
portions of the same piece. The slowness of the transfusion 
of moisture through the wood is an important factor. This 
varies with different woods and greatly in different direc- 
tions. Wood becomes soft and plastic when hot and moist, 
and will yield more or less to internal stresses. As some 
species are practically impervious to air when wet, this 
plasticity of the cell walls causes them to collapse as the 
water passes outward from the cell cavities. This dif- 
ficulty has given much trouble in the case of Western red 
cedar, and also to some extent in redwood. The unequal 
shrinkage causes internal stresses in the wood as it dries, 
which results in warping, checking, case-hardening, and 
honeycombing. Case-hardening is one of the naost com- 
mon defects in improperly dried lumber. It is clearly 
shown by the cupping of the two halves when a case- 
hardened board is resawed. Chemical changes also occur 
in the wood in drying, especially so at higher temperatures, 
rendering it less hygroscopic, but more brittle. If dried 
too much or at too high a temperature, the strength and 
toughness is seriously reduced, 

Conditions of Success 

Commercial success in drying therefore requires that 
the substance be exposed to the air in the most efficient 
manner; that the temperature of the air be as high as the 


substance will stand without injury, and that the air change 
or movement be as rapid as is consistent with economical 
installation and operation. Conditions of success there- 
fore require the observance of the following points, which 
embody the basic principles of the process: (1) The 
timber should be heated through before drying begins. 
(2) The air should be very humid at the beginning of the 
drying process, and be made drier only gradually. (3) The 
temperature of the lumber must be maintained uniformly 
throughout the entire pile. (4) Control of the drying 
process at any given temperature must be secured by 
controlling the relative humidity, not by decreasing the 
circulation. (5) In general, high temperatures permit 
more rapid drying than do. lower temperatures. The 
higher the temperature of the lumber, the more efficient 
is the kiln. It is believed that temperatures as high as 
the boiling point are not injurious to most woods, pro- 
viding all other fundamentally important features are 
taken care of. Some species, however, are not able to 
stand as high temperatures as others, and (6) the degree 
of dryness attained, where strength is the prime requisite, 
should not exceed that at which the wood is to be used. 

Different Treatment according to Kind 

The rapidity with which water may be evaporated, that 
is, the rate of drying, depends on the size and shape of 
the piece and on the structure of the wood. Thin stock 
can be dried much faster than thick, under the same con- 
ditions of temperature, circulation, and humidity. Pine 
can be dried, as a general thing, in about one third of the 
time that would be required for oak of the same thickness, 
although the former contains the more water of the two. 
Quarter-sawn oak usually requires half again as long as 
plain oak. Mahogany requires about the same time as 
plain oak; ash dries in a little less time, and maple, accord- 
ing to the purpose for which it is intended, may be dried 
in one fifth the time needed for oak, or may require a 
slightly longer treatment. For birch, the time required 
is from one half to two thirds, and for poplar and bass- 
wood, from one fifth to one third that required for oak. 


All kinds and thicknesses of lumber cannot be dried at 
the same time in the same kiln. It is manifest that green 
and air-dried lumber, dense and porous lumber, all re- 
quire different treatment. For instance. Southern yellow 
pine when cut green from the log will stand a very high 
temperature, say 200 degrees Fahrenheit, and in fact this 
high temperature is necessary together with a rapid circula- 
tion of air in order to neutralize the acidity of the pitch 
which causes the wood to blue and discolor. This lumber 
requires to be heated up immediately and to be kept hot 
throughout the length of the kiln. Hence the kiln must 
not be of such length as to allow of the air being too much 
cooled before escaping. 

Temperature depends 

While it is true that a higher temperature can be carried 
in the kiln for drying pine and similar woods, this does 
not altogether account for the great difference in drying 
time, as experience has taught us that even when both 
woods are dried in the same kiln, under the same condi- 
tions, pine will still dry much faster, proving thereby that 
the structure of the wood itself affects drying. 

The aim of all kiln designers should be to dry in the 
shortest possible time, without injury to the material. Ex- 
perience has demonstrated that high temperatures are very 
effective in evaporating water, regardless of the degree of 
humidity, but great care must be exercised in using ex- 
treme temperatures that the material to be dried is not 
damaged by checking, case-hardening, or hollow-horning. 

The temperature used should depend upon the species 
and condition of the material when entering the kiln. In 
general, it is advantageous to have as high a temperature 
as possible, both for economy of operation and speed of 
drying, but the physical properties of the wood will govern 

Many species cannot be dried satisfactorily at high 
temperatures on account of their peculiar behavior. This 
is particularly so with green lumber. 

Air-dried wood will stand a relatively higher tempera- 
ture, as a rule, than wet or green wood. In drying green 


wood direct from the saw, it is usually best to start with 
a comparatively low temperature, and not raise the tem- 
perature until the wood is nearly dry. For example, 
green maple containing about 60 per cent of its dry weight 
in water should be started at about 120 degrees Fahrenheit 
and when it reaches a dryness of 25 per cent, the tempera- 
ture may be raised gradually up to 190 degrees. 

It is exceedingly important that the material be prac- 
tically at the same temperature throughout if perfect 
drying is to be secured. It should be the same tempera- 
ture in the center of a pile or car as on the outside, and 
the same in the center of each individual piece of wood 
as on its surface. This is the effect obtained by natural 
air-drying. The outside atmosphere and breezes (natural 
air circulation) are so ample that the heat extracted for 
drying does not appreciably change the temperature. 

When once the wood has been raised to a high tem- 
perature through and through and especially when the 
surface has been rendered most permeable to moisture, 
drying may proceed as rapidly as it can be forced by arti- 
ficial circulation, provided the heat lost from the wood 
through vaporization is constantly replaced by the heat 
of the kiln. 

It is evident that to secure an even temperature, a free 
circulation of air must be brought in contact with the 
wood. It is also evident that in addition to heat and a 
circulation of air, the air must be charged with a certain 
amount of moisture to prevent surface drying or case- 

There are some twenty-five different makes of dry kilns 
on the market, which fulfill to a varying degree the funda- 
mental requirements. Probably none of them succeed 
perfectly in fulfilling all. 

It is well to have the temperature of a dry kiln con- 
trolled by a thermostat which actuates the valve on the 
main steam supply pipe. It is doubly important to main- 
tain a uniform temperature and avoid fluctuations in 
the dry kiln, since a change in temperature will greatly 
alter the relative humidity. 

In artificial drying, temperatures of from 150 to 180 de- 


grees Fahrenheit are usually employed. Pine, spruce, 
cypress, cedar, etc., are dried fresh from the saw, allowing 
four days for 1-inch stuff. Hardwoods, especially oak, ash, 
maple, birch, sycamore, etc., are usually air-seasoned for 
three to six months to allow the first shrinkage to take place 
more gradually, and are then exposed to the above tem- 
peratures in the kiln for about six to ten days for 1-inch 
stuff, other dimensions in proportion. 

Freshly cut poplar and cottonwood are often dried 
direct from the saw in a kiln. By employing lower tem- 
peratures, 100 to 120 degrees Fahrenheit, green oak, ash, 
etc., can be seasoned in dry kilns without much injury to 
the material. 

Steaming and sweating the wood is sometimes resorted 
to in order to prevent checking and case-hardening, but 
not, as has been frequently asserted, to enable the material 
to dry. 

Air Circulation 

Air circulation is of the utmost importance, since no 
drying whatever can take place when it is lacking. The 
evaporation of moisture requires heat and this must be 
suppUed by the circulating air. Moreover, the moisture 
laden air must be constantly removed and fresh, drier air 
substituted. Probably this is the factor which gives 
more trouble in commercial operations than anything 
else, and the one which causes the greatest number of 

It is necessary that the air circulate through every 
part of the kiln and that the moving air come in contact 
with every portion of the material to be dried. In fact, 
the humidity is dependent upon the circulation. If the 
air stagnates in any portion of the pile, then the tempera- 
ture will drop and the humidity rise to a condition of 
saturation. Drying will not take place at this portion 
of the pile and the material is apt to mould and rot. 

The method of pihng the material on trucks or in the 
kiln, is therefore, of extreme importance. Various methods 
are in use. Ordinary flat pihng is probably the poorest. 
Flat pihng with open chimney spaces in the piles is better. 


But neither method is suitable for a kiln in which the 
circulation is mainly vertical. 

Edge piling with stickers running vertically is in use 
in kilns when the heating coils are beneath. This is much 

Air being cooled as it comes in contact with a pile of 
material, becomes denser, and consequently tends to sink. 
Unless the material to be dried is so arranged that the 
air can pass gradually downward through the pile as it 
cools, poor circulation is apt to result. 

In edge-piled lumber, with the heating system beneath 
the piles, the natural tendency of the cooled air to descend 
is opposed by the hot air beneath which tends to rise. 
An indeterminate condition is thus brought about, re- 
sulting in non-uniform drying. It has been found that 
air will rise through some layers and descend through 


Humidity is of prime importance because the rate of 
drying and prevention of checking and case-hardening 
are largely dependent thereon. It is generally true that 
the surface of the wood should not dry more rapidly than 
the moisture transfuses from the center of the piece to 
its surface, otherwise disaster will result. As a sufficient 
amount of moisture is removed from the wood to main- 
tain the desired humidity, it is not good economy to 
generate moisture in an outside apparatus and force it 
into a kiln, unless the moisture in the wood is not sufficient 
for this purpose; in that case provision should be made 
for adding any additional moisture that may be required. 

The rate of evaporation may best be controlled by 
controlling the amount of vapor present in the air (relative 
humidity); it should not be controlled by reducing the 
air circulation, since a large circulation is needed at all 
times to supply the necessary heat. 

The humidity should be graded from 100 per cent at 
the receiving end of the kiln, to whatever humidity cor- 
responds with the desired degree of dryness at the de- 
livery end. 


The kiln should be so designed that the proper degree 
may be maintained at its every section. 

A fresh piece of sapwood will lose weight in boiling 
water and can also be dried to quite an extent in steam. 
This proves conclusively that a high degree of humidity 
does not have the detrimental effect on drying that is 
commonly attributed to it. In fact, a proper degree of 
humidity, especially in the loading or receiving end of a 
kiln, is just as necessary to good results in drying as 
getting the proper temperature. 

Experiments have demonstrated also that injury to 
stock in the way of checking, warping, and hollow-horning 
always develops immediately after the stock is taken into 
the kiln, and is due to the degree of humidity being too 
low. The receiving end of the kiln should always be 
kept moist, where the stock has not been steamed before 
being put into the kiln. The reason for this is simple 
enough. When the air is too dry it tends to dry the out- 
side of the material first — which is termed "case-harden- 
ing" — ^ and in so doing shrinks and closes up the pores 
of the wood. As the stock is moved down the kiln, it 
absorbs a continually increasing amount of heat, which 
tends to drive off the moisture still present in the center 
of the stock. The pores on the outside having been closed 
up, there is no exit for the vapor or steam that is being 
rapidly formed in the center. It must find its way out 
some way, and in doing so sets up strains, which result 
either in checking, warping, or hollow-horning. If the 
humidity had been kept higher, the outside of the material 
would not have dried so quickly, and the pores would 
have remained open for the exit of moisture from the in- 
terior of the wood, and this trouble would have been 

Where the humidity is kept at a high point in the re- 
ceiving end of the kiln, a higher rate of temperature may 
also be carried, and in that way the drying process is 
hastened with comparative safety. 

It is essential, therefore, to have an ample supply of 
heat through the convection currents of the air; but in 
the case of wood the rate of evaporation must be con- 


trolled, else checking will occur. This can be done by 
means of the relative humidity, as stated before. It is 
clear now that when the air — or, more properly speak- 
ing, the space — is completely saturated no evaporation 
can take place at the given temperature. By reducing 
the humidity, evaporation takes place more and more 

Another bad feature of an insufficient and non-uniform 
supply of heat is that each piece of wood will be heated to 
the evaporating point on the outer surface, the inside 
remaining cool until considerable drying has taken place 
from the surface. Ordinarily in dry kilns high humidity 
and large circulation of air are antitheses to one another. 
To obtain the high humidity the circulation is either 
stopped altogether or greatly reduced, and to reduce the 
humidity a greater circulation is induced by opening the 
ventilators or otherwise increasing the draft. This is 
evidently not good practice, but as a rule is unavoidable 
in most dry kilns of present make. The humidity should 
be raised to check evaporation without reducing the 
circulation if possible. 

While thin stock, such as cooperage and box stuff is 
less inclined to give trouble by undue checking than 1-inch 
and thicker, one will find that any dry kiln will give more 
uniform results and, at the same time, be more economi- 
cal in the use of steam, when the humidity and temperature 
is carried at as high a point as possible without injury to 
the material to be dried. 

Any well-made dry kiln which will fulfill the conditions 
required as to circulation and humidity control should work 
satisfactorily; but each case must be studied by itself, 
and the various factors modified to suit the peculiar con- 
ditions of the problem in hand. In every new case the 
material should be constantly watched and studied and, 
if checking begins, the humidity should be increased until 
it stops. It is not reducing the circulation, but adding 
the necessary moisture to the air, that should be depended 
on to prevent checking. For this purpose it is well to 
have steam jets in the kiln so that if needed they are ready 
at hand. 



There are two distinct ways of handling material in 
dry kilns. One way is to place the load of lumber in a 
chamber where it remains in the same place throughout 
the operation, while the conditions of the drying medium 
are varied as the drying progresses. This is the "apart- 
ment" kiln or stationary method. The other is to run 
the lumber in at one end of the chamber on a wheeled 
truck and gradually move it along until the drying process 
is completed, when it is taken out at the opposite end of 
the kiln. It is the usual custom in these kilns to main- 
tain one end of the chamber moist and the other end 
dry. This is known as the "progressive" type of kiln, 
and is the one most commonly used in large operations. 

It is, however, the least satisfactory of the two where 
careful drying is required, since the conditions cannot 
be so well regulated and the temperatures and humidities 
are apt to change with any change of wind. The apartment 
method can be arranged so that it will not require any 
more kiln space or any more handling of lumber than the 
progressive type. It does, however, require more in- 
telligent operation, since the conditions in the drying 
chamber must be changed as the drying progresses. With 
the progressive type the conditions, once properly es- 
tablished, remain the same. 

To obtain draft or circulation three methods are in use — 
by forced draft or a blower usually placed outside the kiln, 
by ventilation, and by internal circulation and condensa- 
tion. A great many patents have been taken out on 
different methods of ventilation, but in actual operation 
few kihis work exactly as intended. Frequently the air 
moves in the reverse direction for which the ventilators 
were planned. Sometimes a condenser is used in con- 
nection with the blower and the air is re-circulated. It is 
also — and more satisfactorily — used with the gentle 
internal-gravity currents of air. 

Many patents have been taken out for heating systems. 
The differences among these, however, have more to do 
with the mechanical construction than with the process 


of drying. In general, the heating is either direct or in- 
direct. In the former steam coils are placed in the chamber 
with the lumber, and in the latter the air is heated by 
either steam coils or a furnace before it is introduced into 
the drying chamber. 

Moisture is sometimes supplied by means of free 
steam jets in the kiln or in the entering air; but more 
often the moisture evaporated from the lumber is relied 
upon to maintain the humidity necessary. 

A substance becomes dry by the evaporation of its 
inherent moisture into the surrounding space. If this 
space be confined it soon becomes saturated and the proc- 
ess stops. Hence, constant change is necessary in order 
that the moisture given off may be continually carried 

In practice, air movement is therefore absolutely es- 
sential to the process of drying. Heat is merely a useful 
accessory which serves to decrease the time of drying 
by increasing both the rate of evaporation and the ab- 
sorbing power of the surrounding space. 

It makes no difference whether this space is a vacuum 
or filled with air; under either condition it will take up 
a stated weight of vapor. From this it appears that the 
vapor molecules find sufficient space between the molecules 
of air. But the converse is not true, for somewhat less 
air will be contained in a given space saturated with vapor 
than in one devoid of moisture. In other words the air 
does not seem to find sufficient space between the mole- 
cules of vapor. 

If the temperature of the confined space be increased, 
opportunity will thereby be provided for the vaporiza- 
tion of more water, but if it be decreased, its capacity for 
moisture will be reduced and visible water will be de- 
posited. The temperature at which this takes place is 
known as the "dew-point" and depends upon the initial 
degree of saturation of the given space ; the less the relative 
saturation the lower the dew-point. 

Careful piling of the material to be dried, both in the 
yard and dry kiln, is essential to good results in drying. 

Air-dried material is not dry, and its moisture is too 



unevenly distributed to insure good behavior after manu- 

It is quite a difficult matter to give specific or absolute 
correct weights of any species of timber when thoroughly 
or properly dried, in order that one may be guided in 
these kiln operations, as a great deal depends upon the 
species of wood to be dried, its density, and upon the 
thickness which it has been cut, and its condition when 
entering the drying chamber. 

Elm will naturally weigh less than beech, and where 
the wood is close-grained or compact it will weigh more 
than coarse-grained wood of the same species, and, there- 
fore, no set rules can be laid down, as good judgment 
only should be used, as the quality of the drying is not 
purely one of time. Sometimes the comparatively slow 
process gives excellent results, while to rush a lot of stock 
through the kiln may be to turn it out so poorly seasoned 
that it will not give satisfaction when worked into the 
finished product. The mistreatment of the material in 
this respect results in numerous defects, chief among which 
are warping and twisting, checking, case-hardening, and 
honeycombing, or, as sometimes called, hollow-horning. 

Since the proportion of sap and heartwood varies with 
size, age, species, and individual trees, the following figures 
as regards weight must be regarded as mere approxi- 
mations : 

Pounds of Water Lost in Drying 100 Pounds of Green Wood 
IN THE Kiln 

or interior 



(1) Pine, cedar, spruce, and fir 

(2) Cypress, extremely variable 

(3) Poplar, cottonwood, and basswood 

(4) Oak, beech, ash, maple, birch, elm, hickory, 

chestnut, walnut, and sycamore 

The lighter kinds have the most water in the sapwood; 
thus sycamore has more water than hickory, etc. 

The efficiency of the drying operations depends a great 


deal upon the way in which the lumber is piled, especially 
when the humidity is not regulated. From the theory 
of drying it is evident that the rate of evaporation in dry 
kilns where the humidity is not regulated depends entirely 
upon the rate of circulation, other things being equal. 
Consequently, those portions of the wood which receive 
the greatest amount of air dry the most rapidly, and 
vice versa. The only way, therefore, in which anything 
like uniform drying can take place is where the lumber is 
so piled that each portion of it comes in contact with the 
same amount of air. 

In the Forestry Service kiln (Fig. 30), where the degree of 
relative humidity is used to control the rate of drying, 
the amount of circulation makes little difference, pro- 
vided it exceeds a certain amount. It is desirable to pile 
the lumber so as to offer as little frictional resistance as 
possible and at the same time secure uniform circulation. 
If circulation is excessive in any place it simply means 
waste of energy but no other injury to the lumber. 

The best method of piling is one which permits the 
heated air to pass through the pile in a somewhat down- 
ward direction. The natural tendency of the cooled air 
to descend is thus taken advantage of in assisting the 
circulation in the kiln. This is especially important when 
cold or green lumber is first introduced into the kiln. 
But even when the lumber has become warmed the cool- 
ing due to the evaporation increases the density of the 
mixture of the air and vapor. 

Kiln-drying Gum 

The following article was published by the United 
States Forestry Service as to the best method of kiln- 
drying gum: 

Piling. ^ — ^ Perhaps the most important factor in good kiln- 
drying, especially in the case of the gums, is the method of 
piling. It is our opinion that proper and very careful piling 
will greatly reduce the loss due to warping. A good method 
of piling is to place the lumber length-wise of the kiln and 
on an incline cross-wise. The warm air should rise at 


the higher side of the pile and descend between the courses 
of lumber. The reason for this is very simple and the 
principle has been applied in the manufacture of the best 
ice boxes for some time. The most efficient refrigerators 
are iced at the side, the ice compartment opening to the 
cooling chamber at the top and bottom. The warm air 
from above is cooled by melting the ice. It then becomes 
denser and settles down into the main chamber. The 
articles in the cooling room warm the air as they cool, so 
it rises to the top and again comes in contact with the 
ice, thus completing the cycle. The rate of this natural 
circulation is automatically regulated by the temperature 
of the articles in the cooling chamber and by the amount 
of ice in the icing compartment; hence the efficiency of 
such a box is high. 

Now let us apply this principle to the drying of lumber. 
First we must understand that as long as the lumber is 
moist and drying, it will always be cooler than the sur- 
rounding air, the amount of this difference being determined 
by the rate of drying and the moisture in the wood. As 
the lumber dries, its temperature gradually rises until it 
is equal to that of the air, when perfect dryness results. 
With this fact in mind it is clear that the function of the 
lumber in a kiln is exactly analogous to that of the ice in 
an ice box; that is, it is the cooling agent. Similarly, 
the heating pipes in a dry kiln bring about the same effect 
as the articles of food in the ice box in that they serve to 
heat the air. Therefore, the air will be cooled by the 
lumber, causing it to pass downward through the piles. 
If the heating units are placed at the sides of the kiln, 
the action of the air in a good ice box is duplicated in the 
kiln. The significant point in this connection is that, the 
greener and colder the lumber, the faster is the circula- 
tion. This is a highly desirable feature. 

A second vital point is that as the wood becomes grad- 
ually drier the circulation automatically decreases, thus 
resulting in increased efficiency, because there is no need 
for circulation greater than enough to maintain the hu- 
midity of the air as it leaves the lumber about the same 
as it enters. Therefore, we advocate either the longitu- 


tudinal side-wise inclined pile or edge stacking, the latter 
being much preferable when possible. Of course the 
piles in our kiln were small and could not be weighted 
properly, so the best results as to reducing warping were 
not obtained. 

Preliminary Steaming. — Because the fibres of the gums 
become plastic while moist and hot without causing de- 
fects, it is desirable to heat the air-dried lumber to about 
200 degrees Fahrenheit in saturated steam at atmospheric 
pressure in order to reduce the warping. This treatment 
also furnishes a means of heating the lumber very rapidly. 
It is probably a good way to stop the sap-staining of green 
lumber, if it is steamed while green. We have not investi- 
gated the other effects of steaming green gum, however, 
so we hesitate to recommend it. 

Temperatures as high as 210 degrees Fahrenheit were used 
with no apparent harm to the material. The best result 
was obtained with the temperature of 180 degrees Fahren- 
heit, after the first preliminary heating in steam to 200 
degrees Fahrenheit, Higher temperatures may be used 
with air-dried gum, however. 

The best method of humidity control proved to be to 
reduce the relative humidity of the air from 100 per cent 
(saturated steam) very carefully at first and then more 
rapidly to 30 per cent in about four days. If the change 
is too marked immediately after the steaming period, 
checking will invariably result. Under these temperature 
and humidity conditions the stock was dried from 15 
per cent moisture, based on the dry wood weight, to 6 per 
cent in five days' time. The loss due to checking was 
about 5 per cent, based on the actual footage loss, not on 
commercial grades. 

Final Steaming . — From time to time during the test 
runs the material was resawed to test for case-hardening. 
The stock dried in five days showed slight case-hardening, 
so it was steamed at atmospheric pressure for 36 minutes 
near the close of the run, with the result that when dried 
off again the stresses were no longer present. The mate- 
rial from one run was steamed for three hours at atmos- 


pheric pressure and proved very badly case-hardened, but 
in the reverse direction. It seems possible that by test- 
ing for the amount of case-hardening one might select 
a final steaming period which would eliminate all stresses 
in the wood. 

Kiln-drying of Green Red Gum 

The following article was pubhshed by the United 
States Forestry Service on the kiln-drying of green red 

A short time ago fifteen fine, red-gum logs 16 feet long 
were received from Sardis, Miss. They were in excellent 
condition and quite green. 

It has been our belief that if the gum could be kiln- 
dried directly from the saw, a number of the difficulties 
in seasoning might be avoided. Therefore, we have under- 
taken to find out whether or not such a thing is feasible. 
The green logs now at the laboratory are to be used in 
this investigation. One run of a prehminary nature has 
just been made, the method and results of which I will 
now tell. 

This method was really adapted to the drying of Southern 
pine, and one log of the green gum was cut into 1-inch 
stock and dried with the pine. The heartwood contained 
many knots and some checks, although it was in general 
of quite good quahty. The sapwood was in fine condition 
and almost as white as snow. 

This material was edge-stacked with one crosser at 
either end and one at the center of the 16-foot board. 
This is sufficient for the pine, but was absolutely inadequate 
for drying green gum. A special shrinkage take-up was 
applied at the three points. The results proved very 
interesting in spite of the warping which \N^as expected 
with but three crossers in 16 feet. The method of cir- 
culation described was used. It is our behef that edge 
piling is best for this method. 

This method of kiln-drying depends on the maintenance 
of a high velocity of slightly superheated steam through 
the lumber. In few words, the object is to maintain the 
temperature of the vapor as it leaves the lumber at slightly 


above 212 degrees Fahrenheit. In order to accomplish this 
result, it is necessary to maintain the high velocity of 
circulation. As the wood dries, the superheat may be 
increased until a temperature of 225 degrees or 230 degrees 
Fahrenheit of the exit air is recorded. 

The 1-inch green gum was dried from 20.1 per cent to 
11.4 per cent moisture, based on the dry wood weight in 
45 hours. The loss due to checking was 10 per cent. 
Nearly every knot in the heartwood was checked, show- 
ing that as the knots could be eliminated in any case, this 
loss might not be so great. It was significant that practi- 
cally all of the checking occurred in the heartwood. The 
loss due to warping was 22 per cent. Of course this was 
large; but not nearly enough crossers were used for the 
gum. It is our opinion that this loss due to warping can 
be very much reduced by using at least eight crossers and 
providing for taking up of the shrinkage. A feature of 
this process which is very important is that the method 
absolutely prevents all sap staining. 

Another delightful surprise was the manner in which 
the superheated steam method of drying changed the 
color of the sapwood from pure white to a beautifully 
uniform, clean-looking, cherry red color which very closely 
resembles that of the heartwood. This method is not 
new by any means, as several patents have been granted 
on the steaming of gum to render the sapwood more nearly 
the color of the heartwoods. The method of application 
in kiln-drying green gum we believe to be new, however. 
Other methods for kiln-drying this green stock are to be 
tested until the proper process is developed. We ex- 
pect to have something interesting to report in the near 

1 The above test was made at the United States Forestry Service Laboratory, 
Madison, Wis. 




Dry kilns as in use to-day are divided into two classes: 
The "pipe" or "moist-air" kiln, in which natural draft 
is relied upon for circulation and, the "blower" or "hot 
blast" kiln, in which the circulation is produced by fans 
or blowers. Both classes have their adherents and either 
one will produce satisfactory results if properly operated. 

The "Blower" or "Hot Blast" Kiln 

The blower kiln in its various types has been in use so 
long that it is hardly necessary to give to it a lengthy in- 
troduction. These kilns at their inauguration were a 
wonderful improvement over the old style "bake-oven" 
or "sweat box" kiln then employed, both on account of 
the improved quahty of the material and the rapidity at 
which it was dried. 

These blower kilns have undergone steady improvement, 
not only in the apparatus and equipment, but also in their 
general design, method of introducing air, and provision 
for controUing the temperature and humidity. With this 
type of kiln the circulation is always under absolute con- 
trol and can be adjusted to suit the conditions, which 
necessarily vary with the conditions of the material to 
be dried and the quantity to be put through the kiln. 

In either the blower or moist-air type of dry kiln, how- 
ever, it is absolutely essential, in order to secure satis- 
factory results, both as to rapidity in drying and good 
quaUty of stock, that the kiln be so designed that the 
temperature and humidity, together with circulation, are 
always under convenient control. Any dry kiln in which 
this has not been carefully considered will not give the 
desired results. 


In the old style blower kiln, while the circulation and 
temperature was very largely under the operator's con- 
trol, it was next to impossible to produce conditions in 
the receiving end of the kiln so that the humidity could 
be kept at the proper point. In fact, this was one reason 
why the natural draft, or so-called moist-air kiln was 

The advent of the moist-air kiln served as an education 
to kiln designers and manufacturers, in that it has shown 
conclusively the value of a proper degree of humidity in 
the receiving end of any progressive dry kiln, and it has 
been of special benefit also in that it gave the manufacturers 
of blower kilns an idea as to how to improve the design 
of their type of kiln to overcome the difficulty referred to 
in the old style blower kilns. This has now been remedied, 
and in a decidedly simple manner, as is usually the case 
with all things that possess merit. 

It was found that by returning from one third to one 
half of the moist air after having passed through the kiln 
back to the fan room and by mixing it with the fresh and 
more or less dry air going into the drying room, ma^the j? 
humidity could be kept under convenient control. -^ 

The amount of air that can be returned from a kiln of 
this class depends upon three things: (1) The condition 
of the material when entering the drying room; (2) the 
rapidity with which the material is to be dried; and (3) the 
condition of the outside atmosphere. In the winter season 
it will be found that a larger proportion of air may be 
returned to the drying room than in summer, as the air 
during the winter season contains considerably less mois- 
ture and as a consequence is much drier. This is rather a 
fortunate coincidence, as, when the kiln is being operated 
in this manner, it will be much more economical in its 
steam consumption. 

In the summer season, when the outside atmosphere is 
saturated to a much greater extent, it will be found that 
it is not possible to return as great a quantity of air to the 
drying room, although there have been instances of kilns 
of this class, which in operation have had all the air re- 
turned and found to give satisfactory results. This is 


an unusual condition, however, and can only be accounted 
for by some special or peculiar condition surrounding the 

In some instances, the desired amount of humidity m a 
blower type of kiln is obtained by the addition of a steam 
spray in the receiving end of the kiln, much in the same 
manner as that used in the moist-air kilns. This method 
is not as economical as returning the moisture-laden air 
from the drying room as explained in the preceding para- 
graph. 1 • J • 

With the positive circulation that may be obtained in 
a blower kiln, and with the conditions of temperature and 
humidity under convenient control, this type of kiln has 
the elements most necessary to produce satisfactory dry- 
ing in the quickest possible elapsed time. 

It must not be inferred from this, however, that this 
class of dry kiln may be installed and satisfactory re- 
sults obtained regardless of how it is handled. A great 
deal of the success of any dry kiln — or any other 
apparatus, for that matter — depends upon intelhgent 

Operation of the "Blower" Dry Kiln 

It is essential that the operator be suppUed with proper 
facilities to keep a record of the material as it is placed 
into the drying room, and when it is taken out. An ac- 
curate record should be kept of the temperature every 
two or three hours, for the different thicknesses and species 
of lumber, that he may have some rehable data to guide 
him in future cases. 

Any man possessing ordinary intelhgence can operate 
dry kilns and secure satisfactory results, providing he will 
use good judgment and follow the basic instructions as 
outhned below: 

1. When cold and before putting into operation, heat 

the apparatus slowly until all pipes are hot, then 
start the fan or blower, gradually bringing it up 
to its required speed. 

2. See that all steam supply valves are kept wide open, 


unless you desire to lengthen the time required to 
dry the material. 

3. When using exhaust steam, the valve from the 

header (which is a separate drip, independent of 
the trap connection) must be kept wide open, but 
must be closed when live steam is used on that 
part of the heater. 

4. The engines as supplied by the manufacturers are 

constructed to operate the fan or blower at a proper 
speed with its throttle valve wide open, and with 
not less than 80 pounds pressure of steam. 

5. If the return steam trap does not discharge regularly, 

it is important that it be opened and thoroughly 
cleaned and the valve seat re-ground. 

6. As good air circulation is as essential as the proper 

degree of heat, and as the volume of air and its 
contact with the material to be dried depends upon 
the volume delivered by the fan or blower, it is 
necessary to maintain a regular and uniform speed 
of the engine. 

7. Atmospheric openings must always be maintained 

in the fan or heater room for fresh air supply. 

8. Successful drying cannot be accomplished without 

ample and free circulation of air at all times. 
If the above instructions are fully carried out, and good 
judgment used in the handling and operation of the 
blower kiln, no difficulties should be encountered in suc- 
cessfully drying the materials at hand. 

The "Pipe" or "Moist-air" Dry Kiln 

While in the blower class of dry kiln, the circulation is 
obtained by forced draft with the aid of fans or blowers, 
in the Moist-air kilns (see Fig. 31); the circulation is ob- 
tained by natural draft only, aided by the manipulation 
of dampers installed at the receiving end of the drying 
room, which lead to vertical flues through a stack to the 
outside atmosphere. 

The heat in these kilns is obtained by condensing steam 
in coils of pipe, which are placed underneath the material 



to be dried. As the degree of heat required, and steam 
pressure govern the amount of radiation, there are several 
types of radiating coils. In Fig. 32 will be seen the Single 
Row Heating Coils for live or high pressure steam, which 
are used when the low temperature is required. Figure 33 
shows the Double (or 2) Row Heating Coils for live or 
high pressure steam. This apparatus is used when a 

Fig. 31. Section through a typical Moist-air Dry Kiln. 

medium temperature is required. In Fig. 34 will be seen 
the Vertical Type Heating Coils which is recommended 
where exhaust or low-pressure steam is to be used, or may 
be used with live or high-pressure steam when high tem- 
peratures are desired. 

These heating coils are usually installed in sections, 
which permit any degree of heat from the minimum to 
the maximum to be maintained by the elimination of, 
or the addition of, any number of heating sections. This 
gives a dry kiln for the drying of green softwoods, or by 
shutting off a portion of the radiating coils ' — thus re- 
ducing the temperature — a dry kiln for drying hard- 
woods, that will not stand the maximum degree of heat. 

In the Moist-air or Natural Draft type of dry kiln, any 













degree of huixtidity, from clear and dry to a dense fog may 
be obtained; this is in fact, the main and most important 
feature of this type of dry kiln, and the most essential 
one in the drying of hardwoods. 

It is not generally understood that the length of a kiln 
has any effect upon the quantity of material that may be 
put through it, but it is a fact nevertheless that long kilns 
are much more effective, and produce a better quality of 
stock in less time than kilns of shorter length. 

Experience has proven that a kiln from 80 to 125 feet 
in length will produce the best results, and it should be 
the practice, where possible, to keep them within these 
figures. The reason for this is that in a long kiln there is 
a greater drop in temperature between the discharge end 
and the green or receiving end of the kiln. 

It is very essential that the conditions in the receiving 
end of the kiln, as far as the temperature and humidity 
are concerned, must go hand in hand. 

It has also been found that in a long kiln the desired 
conditions may be obtained with higher temperatures 
than with a shorter kiln; consequently higher tempera- 
tures may be carried in the discharge end of the kiln, 
thereby securing greater rapidity in drying. It is not 
unusual to find that a temperature of 200 degrees Fahrenheit 
is carried in the discharge end of a long dry kiln with 
safety, without in any way injuring the quality of the 
material, although, it would be better not to exceed 180 
degrees in the discharge end, and about 120 degrees in 
the receiving or green end in order to be on the safe side. 

Operation of the "Moist-air" Dry Kiln 

To obtain the best results these kilns should be kept 
in continuous operation when once started, that is, they 
should be operated continuously day and night. When 
not in operation at night or on Sundays, and the kiln is 
used to season green stock direct from the saw, the large 
doors at both ends of the kiln should be opened wide, or 
the material to be dried will ''sap stain." 

It is highly important that the operator attending any 
drying apparatus keep a minute and accurate record of 



O m 


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the condition of the material as it is placed into the drying 
room, and its final condition when taken out. 

Records of the temperature and humidity should be 
taken frequently and at stated periods for the different 
thicknesses and species of material, in order that he may 
have reliable data to guide him in future operations. 

The following facts should be taken into consideration 
when operating the Moist-air dry kiln: 

1. Before any material has been placed in the drying 

room, the steam should be turned into the heating 
or radiating coils, gradually warming them, and 
bringing the temperature in the kiln up to the 
desired degree. 

2. Care should be exercised that there is sufficient 

humidity in the receiving or loading end of the 
kiln, in order to guard against checking, case- 
hardening, etc. Therefore it is essential that the 
steam spray at the receiving or loading end of the 
kiln be properly manipulated. 

3. As the temperature depends principally upon the 

pressure of steam carried in the boilers, maintain 
a steam pressure of not less than 80 pounds at all 
times; it may range as high as 100 pounds. The 
higher the temperature with its relatively high 
humidity the more rapidly the drying will be ac- 

4. Since air circulation is as essential as the proper degree 

of heat, and as its contact with the material to be 
dried depends upon its free circulation, it is nec- 
essary that the dampers for its admittance into, 
and its exit from, the drying room be efficiently 
and properly operated. Successful drying cannot 
be accomplished without ample and free circula- 
tion of air at all times during the drying process. 

If the above basic principles are carefully noted and 
followed out, and good common sense used in the handling 
and operation of the kiln apparatus, no serious difficulties 
should arise against the successful drying of the materials 
at hand. 


Choice of Drying Method 

At this point naturally arises the question: Which of 
the two classes of dry kilns, the "Moist-air" or "Blower" 
kiln is the better adapted for my particular needs? 

This must be determined entirely by the species of 
wood to be dried, its condition when it goes into the kiln, 
and what kind of finished product is to be manufactured 
from it. 

Almost any species of hardwood which has been sub- 
jected to air-seasoning for three months or more may be 
dried rapidly and in the best possible condition for glue- 
jointing and fine finishing with a "Blower" kiln, but green 
hardwood, direct from the saw, can only be successfully 
dried (if at all) in a "Moist-air" kiln. 

Most furniture factories have considerable bent stock 
which must of necessity be thoroughly steamed before 
bending. By steaming, the initial process of the Moist- 
air kiln has been consummated. Hence, the Blower kiln is 
better adapted to the drying of such stock than the Moist- 
air kiln would be, as the stock has been thoroughly soaked 
by the preliminary steaming, and all that is required is 
sufficient heat to volatilize the moisture, and a strong 
circulation of air to remove it as it comes to the surface. 

The Moist-air kiln is better adapted to the drying of 
tight cooperage stock, while the Blower kiln is almost 
universally used throughout the slack cooperage industry 
for the drjdng of its products. 

For the drying of heavy timbers, planks, blocks, carriage 
stock, etc., and for all species of hardwood thicker 
than oiTe inch, the Moist-air kiln is undoubtedly the 

Both types of kilns are equally well adapted to the dry- 
ing of 1-inch green Norway and white pine, elm, hemlock, 
and such woods as are used in the manufacture of flooring, 
ceiling, siding, shingles, hoops, tub and pail stock, etc. 

The selection of one or the other for such work is largely 
a matter of personal opinion. 


Kilns of Different Types 

All dry kilns as in use to-day are divided as to method 
of drying into two classes : 

The 'Tipe" or "Moist-air" kiln; 
The "Blower" or "Hot Blast" kiln; 
both of which have been fully explained in a previous 

The above two classes are again subdivided into five 
different types of dry kilns as follows: 

The "Progressive" kiln; 
The "Apartment" kiln; 
The "Pocket" kiln; 
The "Tower" kiln; 
The "Box" kiln. 

The "Progressive" Dry Kiln 

Dry kilns constructed so that the material goes in at 
one end and is taken out at the opposite end are called 
Progressive dry kilns, from the fact that the material 
gradually progresses through the kiln from one stage to 
another while drying (see Fig. 31). 

In the operation of the Progressive kiln, the material 
is first subjected to a sweating or steaming process at the 
receiving or loading end of the kiln with a low temperature 
and a relative high humidity. It then gradually pro- 
gresses through the kiln into higher temperatures and 
lower humidities, as well as changes of air circulation, 
until it reaches the final stage at the discharge end of the 

Progressive kilns, in order to produce the most satis- 
factory results, especially in the drying of hardwoods or 
heavy softwood timbers, should be not less than 100 feet 
in length (see Fig. 35). 

In placing this type of kiln in operation, the following 
instructions should be carefully followed: 

When steam has been turned into the heating coils, and 
the kiln is fairly warm, place the first car of material to 
be dried in the drying room — preferably in the morn- 








5 g 



ing — about 25 feet from the kiln door on the receiving 
or loading end of the kiln, blocking the wheels so that it 
will remain stationary. 
Five hours later, or 
about noon, run in the 
second car and stop it 
about five feet from the 
first one placed in the 
drying room. Five 
hours later, or in the 
evening push car num- 
ber two up against the 
first car; then run in 
car number three, stop- 
ping it about five feet 
from car number two. 

On the morning of 
the second day, push 
car number three 
against the others, and 
then move them all 
forward about 25 feet, 
and then run in car 
number four, stopping 
it about five feet from 
the car in advance of 
it. Five hours later, or 
about noon, run in car 
number five and stop 
it about five feet from 
car number four. In 
the evening or about 
five hours later, push 
these cars against the 
ones ahead, and run in 

loaded car number six, stopping it about five feet from the 
preceding car. 

On the morning of the third day, move all the cars for- 
ward about six feet; then run in loaded car number seven 
and stop it about four feet from the car preceding it. 

CO rj 

2 ^ 

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Five hours later or about noon push this car against those 
in advance of it, and run in loaded car number eight, 
moving all cars forward about six feet, and continue in 
this manner until the full complement of cars have been 
placed in the kiln. When the kiln has been filled, re- 
move car number one and push all the remaining cars 
forward and run in the next loaded car, and continue in 
this manner as long as the kiln is in operation. 

As the temperature depends principally upon the pres- 
sure of steam, maintain a steam pressure of not less than 
80 pounds at all times; it may range up to as high as 100 
pounds. The higher the temperature with a relatively 
higher humidity the more rapidly the drying will be ac- 

If the above instructions are carried out, the temper- 
atures, humidities, and air circulation properly manip- 
ulated, there should be complete success in the handling 
of this type of dry kiln. 

The Progressive type of dry kiln is adapted to such lines 
of manufacture that have large quantities of material to 
kiln-dry where the species to be dried is of a similiar 
nature or texture, and does not vary to any great extent 
in its thickness, such, for instance, as: 

Oak flooring plants; 

Maple flooring plants; 

Cooperage plants; 

Large box plants; 

Furniture factories; etc. . 

In the selection of this kind of dry kiln, consideration 
should be given to the question of ground space of sufficient 
length or dimension to accomodate a kiln of proper length 
for successful drying. 

The "Apartment" Dry Kiln 

The Apartment system of dry kilns are primarily de- 
signed for the drying of different kinds or sizes of material 
at the same time, a separate room or apartment being 
devoted to each species or size when the quantity is suf- 
ficient (see Fig. 36). 


These kilns are sometimes built single or in batteries 
of two or more, generally not exceeding 40 or 50 feet 
in length with doors and platforms at both ends the same 
as the Progressive kilns; but in operation each kiln is 
entirely filled at one loading and then closed, and the 
entire contents dried at one time, then emptied and again 


Any number of apartments may be built, and each 
apartment may be arranged to handle any number of cars, 


Fig 36 Exterior View of Six Apartment Dry Kilns, each 10 Feet wide by 
52 Feet long, End-wise Piling. They are entirely of fire-proof construc- 
tion and equipped with double doors (Hussey asbestos outside and 
canvas inside), and are also equipped with humidity and air control 
dampers, which may be operated from the outside without opening 
the kiln doors, which is a very good feature. 

generally about three or four, or they may be so con- 
structed that the material is piled directly upon the floor 
of the drying room. 

When cars are used, it is well to have a transfer car at 
each end of the kilns, and stub tracks for holding cars of 
dry material, and for the loading of the unseasoned stock, 
as in this manner the kilns may be kept in full operation 
at all times. 

In this type of dry kiln the material receives the same 


treatment and process that it would in a Progressive kiln. 
The advantages of Apartment kilns is manifest where 
certain conditions require the drying of numerous kinds 
as well as thicknesses of material at one and the same time. 
This method permits of several short drying rooms or 
apartments so that it is not necessary to mix hardwoods 
and softwoods, or thick and thin material in the same kiln 

In these small kilns the circulation is under perfect 
control, so that the efficiency is equal to that of the more 
extensive plants, and will readily appeal to manufacturers 
whose output calls for the prompt and constant seasoning 
of a large variety of small stock, rather than a large volume 
of material of uniform size and grade. 

Apartment kilns are recommended for industries where 
conditions require numerous kinds and thicknesses of 
material to be dried, such as: 

Furniture factories; 
Piano factories; 
Interior woodwork mills; 
Planing mills; etc. 

The "Pocket" Dry Kiln 

"Pocket" dry kilns (see Fig. 37) are generally built in 
batteries of several pockets. They have the tracks level 
and the lumber goes in and out at the same end. Each 
drying room is entirely filled at one time, the material is 
dried and then removed and the kiln again recharged. 

The length of "Pocket" kilns ranges generally from 
14 feet to about 32 feet. 

The interior equipment for this type of dry kiln is 
arranged very similiar to that used in the Apartment 
kiln. The heating or radiating coils and steam spray 
jets extend the whole length of the drying room, and are 
arranged for the use of either hve or exhaust steam, as 

Inasmuch as Pocket kilns have doors at one end only, 
this feature ehminates a certain amount of door exposure, 
which conduces towards economy in operation. 



In operating Pocket kilns, woods of different texture 
and thickness should be separated and placed in dif- 
ferent drying rooms, and each kiln adjusted and operated 





















































































to accommodate the peculiarities of the species and thickness 
of the material to be dried. 

Naturally, the more complex the conditions of manu- 
facturing wood products in any industry, the more dif- 


ficult will be the proper drying of same. Pocket kilns, 
are, therefore, recommended for factories having several 
different kinds and thicknesses of material to dry in small 
quantities of each, such as: • , 

Planing mills; 

Chair factories; 

Furniture factories; 

Sash and door factories; etc. 

The "Tower" Dry Kiln 

The so-called "Tower" dry kiln (see Fig. 38) is de- 
signed for the rapid drying of small stuff in quantities. 
Although the general form of construction and the capacity 
of the individual bins or drying rooms may vary, the same 
essential method of operation is common to all. That is, 
the material itself, such as wooden novelties, loose staves, 
and heading for tubs, kits, and pails, for box stuff, kindling 
wood, etc., is dumped directly into the drying rooms 
from above, or through the roof, in such quantities as 
effectually to fill the bin, from which it is finally removed 
when dry, through the doors at the bottom. 

These dry kilns are usually operated as "Blower" kilns, 
the heating apparatus is generally located in a separate 
room or building adjacent to the main structure or drying 
rooms, and arranged so that the hot air discharged through 
the inlet duct (see illustration) is thoroughly distributed 
beneath a lattice floor upon which rests the material to 
be dried. Through this floor the air passes directly up- 
ward, between and around the stock, and finally returns 
to the fan or heating room. 

This return air duct is so arranged that by means of 
dampers, leading from each drying room, the air may be 
returned in any quantity to the fan room where it is mixed 
with fresh air and again used. This is one of the main 
features of ecomony of the blower system of drying, as 
by the employment of this return air system, considerable 
saving may be made in the amount of steam required for 

The lattice floors in this type of dry kiln are built on 











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03 03 (33 

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an incline, which arrangement materially lessens the cost, 
and increases the convenience with which the dried stock 
may be removed from the bins or drying rooms. 

In operation, the material is conveyed in cars or trucks 
on an overhead trestle — which is inclosed — from which 
the material to be dried is dumped directly into the drying 
rooms or bins, through hoppers arranged for that purpose, 
thereby creating considerable saving in the handling of 
the material to be dried into the kiln. The entire ar- 
rangement thus secures the maximum capacity, with a 
minimum amount of floor space, with the least expense. 
Of course, the higher these kilns are built, the less relative 
cost for a given result in the amount of material dried. 

In some instances, these kilns are built less in height, 
and up against an embankment so that teamloads of 
material may be run directly onto the roof of the kilns, and 
dumped through the hoppers into the drying rooms or 
bins, thus again reducing to a minumim the cost of 
this handling. 

The return air duct plays an important part in both of 
these methods of filling, permitting the air to become 
saturated to the maximum desired, and utilizing much 
of the heat contained therein, which would otherwise 
escape to the atmosphere. 

The ''Tower" kiln is especially adapted to factories 
of the following class: 

Sawmills ; 
Novelty factories; 
Woodenware factories; 
Tub and pail factories; etc. 

The "Box" Dry Kiln 

The ''Box" kiln shown in Figure 39 is an exterior view 
of a kiln of this type which is 20 feet wide, 19 feet deep, 
and 14 feet high, which is the size generally used when 
the space will permit. 

Box kilns are used mostly where only a small quantity 
of material is to be dried. They are not equipped with 
trucks or cars, the material to be dried being piled upon a 



raised platform inside the drying room. This arrange- 
ment, therefore, makes them of less cost than the other 
types of dry kilns. 

They are particularly adapted to any and all species 
and size of lumber to be dried in very small quantities. 

-p f 

pi r 

Pig. 39. Exterior view of the Box Dry Kiln. This particular kiln is 20 feet 
wide, 19 feet deep and 14 feet high. Box kilns are used mostly where 
only a small amount of kiln-dried lumber of various sizes is required. 
They are not equipped with trucks or cars, and therefore cost less to 
construct than any other tjrpe of dry kiln. 

In these small kilns the circulation is under perfect 
control, so that the efficiency is equal to that of the more 
extensive plants. 

These special kilns will readily appeal to manufacturers, 
whose output calls for the prompt and constant seasoning 
of a large variety of small stock, rather than a large volume 
of material of uniform size and grade. 




Within recent years, the edge-wise piling of lumber 
(see Figs. 40 and 41), upon kiln cars has met with con- 
siderable favor on account of its many advantages over 
the older method of flat piling. It has been proven that 
lumber stacked edge-wise dries more uniformly and rapidly, 

Fig. 40. Car Loaded with Lumber on its Edges by the Automatic Stacker, 
to go into the Dry Kiln cross-wise. Equipped with two edge pihng 
kiln trucks. 

and with practically no warping or twisting of the material, 
and that it is finally discharged from the dry kiln in a 
much better and brighter condition. This method of 
piling also considerably increases the holding and con- 
sequent drying capacities of the dry kiln by reason of the 
increased carrying capacities of the kiln cars, and the 
shorter period of time required for drying the material. 


In Figures 42 and 43 are shown different views of the 
automatic lumber stacker for edge-wise piUng of lumber on 
kiln cars. Many users of automatic stackers report that 

Fig 41 Car Loaded with Lumber on its Edges by the Automatic Stacker, 
to go into the Dry Kiln end-wise. The bunks on which the lumber 
rests are channel steel. The end sockets are malleable iron and made 
for I-beam stakes. 

the grade of their lumber is raised to such an extent that 
the system would be profitable for this reason alone, not 
taking into consideration the added saving in time and 
labor, which to anyone's mind should be the most im- 
portant item. 

In operation, the lumber is carried to these automatic 
stackers on transfer chains or chain conveyors, and passes 
on to the stacker table. When the table is covered with 
boards, the "lumber" lever is pulled by the operator, 
which raises a stop, preventing any more lumber leaving 
the chain conveyor. The "table" lever then operates 
the friction drive and raises the table filled with the boards 
to a vertical position. As the table goes up, it raises the 
latches, which fall into place behind the pihng strips that 
had been previously laid on the table. When the table 
returns to the lower position, a new set of piUng strips 
are put in place on the table, and the stream of boards 
which has been accumulating on the conveyor chain are 
again permitted to flow onto the table. As each layer of 
lumber is added, the kiln car is forced out against a strong 



tension. When the car is loaded, binders are put on over 
the stakes by means of a powerful lever arrangement. 

Fig. 42. The above illustration shows the construction of the Automatic 
Lumber Stacker for edge pUing of lumber to go into the dry kiln end- 

Fig. 43. The above illustration shows the construction of the Automatic 
Lumber Stacker for edge piling of lumber to go into the dry kiln cross- 



Fig. 44. The above illustration shows a battery of Three Automatic Lumber 


Fig. 45. The above illustration shows another battery of Three Automatic 

Lumber Stackers. 



Fig. 46. Cars Loaded with Lumber on its Edges by the Automatic Lumber 


After leaving the dry kilns, the loaded car is transferred 
to the unstacker (see Fig. 47). Here it is placed on the 
unstacker car which, by means of a tension device, holds 
the load of lumber tight against the vertical frame of the 
unstacker. The frame of the unstacker is triangular 
and has a series of chains. Each chain has two special 
links with projecting lugs. The chains all travel in unison. 
The lug links engage a layer of boards, sliding the entire 
layer vertically, and the boards, one at a time, fall over 
the top of the unstacker frame onto the inclined table, 
and from there onto conveyor chains from which they 
may be delivered to any point desired, depending upon 
the length and direction of the chain conveyor. 

With these unstackers one man can easily unload a 
kiln car in twenty minutes or less. 

The experience of many users prove that these edge 
stacking machines are not alike. This is important, 
because there is one feature of edge stacking that must 
not be overlooked. Unless each layer of boards is forced 



Fig. 47. The Lumber Unstacker Car, used for unloading cars of Lumber 
loaded by the Automatic Stacker. 

Fig. 48. The Lumber Unstacker Car and Unstacker, used for unloading 
Lumber loaded by the Automatic Stacker. 



into place by power and held under a strong pressure, much 
slack will accumulate in an entire load, and the subsequent 
handling of the kiln cars, and the effect of the kiln-drying 
will loosen up the load until there is a tendency for the 
layers to telescope. And unless the boards are held in 
place rigidly and with strong pressure they will have a 
tendency to warp. 

A kiln car of edge-stacked lumber, properly piled, is 
made up of alternate sohd sheets of lumber and vertical 

Fig. 49. The above illustration shows method of loading kiln cars with 
veneer on its edges by the use of the Tilting Platform. 

open-air spaces, so that the hot air and vapors rise naturally 
and freely through the lumber, drying both sides of the 
board evenly. The distribution of the heat and moisture 
being even and uniform, the drying process is naturally 
quickened, and there is no opportunity or tendency for 
the lumber to warp. 

In Figure 49 will be seen a method of loading kiln cars 
with veneer on edge by the use of a tilting platform. On 
the right of the illustration is seen a partially loaded kiln 
car tilted to an angle of 45 degrees, to facilitate the placing 


of the veneer on the car. At the left is a completely 
loaded car ready to enter the dry kiln. 

Gum, poplar, and pine veneers are satisfactorily dried 
in this manner in from 8 to 24 hom^s. 

In Figure 50 will be seen method of piling lumber on 
the fiat, "cross- wise" of the dry kiln when same has three 

Fig. 50. Method of Loading lumber on its Flat, cross-wise of the Dry 
Kiln when same has Three Tracks. 

In Figure 51 will be seen another method of piUng lum- 
ber on the flat, "cross-wise" of the dry kiln when same 
has three tracks. 

In Figure 52 will be seen method of piUng lumber on the 
flat, "end- wise" of the dry kiln when same has two tracks. 

In Figure 53 will be seen another method of piling lum- 
ber on the flat, "end-wise" of the dry kiln when same has 
two tracks. 

In Figure 54 will be seen method of pihng slack or tight 
barrel staves "cross-wise" of the kiln when same has three 

In Figure 55 will be seen another method of piling slack 
or tight barrel staves "cross- wise" of the dry kiln when 
same has three tracks. 

In Figure 56 will be seen method of piling small tub or 
pail staves "cross-wise" of the dry kiln when same has 
two tracks. 

In Figure 57 will be seen method of piling bundled staves 
"cross-wise" of the dry kiln when same has two tracks. 



Fig. 51. Method of loading Lumber on its Flat, cross-wdse of the Dry Kiln 
when same has Three Tracks. 

Fig. 52. Method of loading Lumber on its Flat, end-wise of the Dry Kiln 
by the Use of the Single-sill or Dolly Truck. 








Fig. 54. Method of loading Kiln Car with Tight or Slack Barrel Staves 
cross-wise of Dry Kiln. 

Fic^ 55. Method of loading Kiln Car with Tight or Slack Barrel Staves 
"^ cross-wise of Dry Kiln. 



Fig. 56. Method of loading Kiln Car with Tub or Pail Staves cross-wise of 

Dry Kiln. 

Fig. 57. Method of loading Kiln Car with Bundled Staves cross-wise of 

Dry Kiln. 



In Figure 58 will be seen method of piling shingles "cross- 
wise" of dry kiln when same has three tracks. 

In Figure 59 will be seen another method of piling 
shingles "cross- wise" of the dry kiln when same has three 

Fig. 58. Method of loading Kiln Car with Shingles cross-wise of Dry Kiln. 

"^ ■■^^^^S£?~~ 

Fig. 59. Method of loading Kiln Car with Shingles cross-wise of Dry Kiln. 



In Figure 60 will be seen method of piling shingles "end- 
wise" of the dry kiln when same has two tracks 

In Figure 61 will be seen a kiln car designed for handling 
short tub or pail staves through a dry kiln. 

Fig. 60. Car loaded with 100,000 Shingles. Equipped with four long end- 
wise piling trucks and to go into dry kiln end- wise. 

Fig. 61. Kiln Car designed for handUng Short Tub or Pail Staves through 

a Dry Kiln. 


In Figure 62 will be seen a kiln car designed for short 
piece stock through a dry kiln. 

In Figure 63 will be seen a type of truck designed for 
the handling of stave bolts about a stave mill or through 
a steam box. 

In Figure 64 will be seen another type of truck designed 
for the handling of stave bolts about a stave mill or through 
a steam box. 

In Figure 65 will be seen another type of truck designed 
for the handling of stave bolts about a stave mill or through 
a steam box. 

In Figure 66 will be seen another type of truck designed 
for the handling of stave bolts about a stave mill or through 
a steam box. 

In Figure 67 will be seen another type of truck designed 
for the handling of stave bolts about a stave mill or through 
a steam box. 

In Figure 68 will be seen another type of truck designed 
for the handling of stave bolts about a stave mill or through 
a steam box. 

In Figure 69 will be seen the Regular 3-rail Transfer 
Car designed for the handling of 2-rail kiln cars which 
have been loaded "end-wise." 

In Figure 70 will be seen another type of Regular 3-rail 
Transfer Car designed for the handling of 2-rail kiln cars 
which have been loaded "end-wise." 

In Figure 71 will be seen a Speciallj^-designed 4-rail 
Transfer Car for 2-rail kiln cars which have been built 
to accommodate extra long material to be dried. 

In Figure 72 will be seen the Regular 2-rail Transfer 
Car designed for the handling of 3-rail kiln cars which have 
been loaded "cross-wise." 

In Figure 73 will be seen another type of Regular 2-rail 
Transfer Car designed for the handling of 3-rail kiln cars 
which have been loaded "cross-wise." 

In Figure 74 will be seen the Regular 2-rail Underslung 
type of Transfer Car designed for the handling of 3-rail 
kiln cars which have been loaded "cross-wise." Two im- 
portant features in the construction of this transfer car 
make it extremely easy in its operation. It has extra large 



^^^ . 

Fig. 62. Kiln Car Designed for handling Short Piece Stock through a Dry Kiln. 

Fig. 63. A Stave Bolt Truck. 






Fig. 66. A Stave Bolt Truck. 

Fig. 67. A Stave Bolt Truck. 


Fig. 68. A Stave Bolt Truck. 

Fig. 69. A Regular 3-Rail Transfer Truck. 



Fig. 70. A Regular 3-Rail Transfer Truck. 

Fig. 71. A Special 4-Rail Transfer Truck. 

Fig. 72. A Regular 2-Rail Transfer Truck. 



Fig. 73. A Regular 2-Rail Transfer Truck. 

Fig. 74. A Regular 2-Rail Underslung Transfer Truck. 

Fig. 75. A Regular 3-Rail Underslung Transfer Truck. 



wheels, diameter 13^ inches, and being underslung, the 
top of its rails are no higher than the other types of transfer 
cars. Note the relative size of the wheels in the illustra- 
tion, yet the car is only about 10 inches in height. 

In Figure 75 will be seen the Regular 3-rail Underslung 
type of Transfer Car designed for the handhng of 2-rail 
kiln cars which have been loaded ''end-wise." This car 
also has the important features of large diameter wheels 
and low rail construction, which make it very easy in its 

Fig. 76. A Special 2-RaiI Flexible Transfer Truck. 

In Figure 76 will be seen the Special 2-rail Flexible 
type of Transfer Car designed for the handhng of 3-rail 
kiln cars which have been loaded "cross-wise." This car 
is equipped with double the usual number of wheels, and 
by making each set of trucks a separate unit (the front 
and rear trucks being bolted to a steel beam with malleable 
iron connection), a shght up-and-down movement is per- 
mitted, which enables this transfer car to adjust itself to 
any unevenness in the track, which is a very good feature. 

In Figure 77 will be seen the Regular Transfer Car de- 
signed for the handling of stave bolt trucks. 

In Figure 78 will be seen another type of Regular Trans- 
fer Car designed for the handling of stave bolt trucks. 

In Figure 79 will be seen a Special Transfer Car de- 
signed for the handling of stave bolt trucks. 



Fig. 77. A Regular Transfer Car for handling Stave Bolt Trucks. 

Fig. 78. A Regular Transfer Car for handling Stave Bolt Trucks. 

Fig. 79. A Special Transfer Car for handling Stave Bolt Trucks. 



In Figure 80 will be seen the Regular Channel-iron 
Kiln Truck designed for edge piling "cross- wise" of the 
dry kiln. 

In Figure 81 will be seen another type of Regular Chan- 
nel-iron Kiln Truck designed for edge piling "cross- wise" 
of the dry kiln. 







1— J 




In Figure 82 will be seen the Regular Channel-iron 
Kiln Truck designed for flat piling "end-wise" of the dry 

Fig. 82. A Regular Channel-iron Kiln Truck. 

Fig. 83. A Regular Channel-iron Kiln Truck. 

Fig. 84. A Regular Single-sill or Dolly Kiln Truck. 

In Figure 83 will be seen the Regular Channel-iron 
Kiln Truck with I-Beam cross-pieces designed for flat 
piling "end- wise" of the dry kiln. 

In Figure 84 will be seen the Regular Small Dolly Kiln 
Truck designed for flat piling "end-wise" of the dry kiln. 



Different Types of Kiln Doors 

In Figure 85 will be seen the Asbestos-lined Door. The 
construction of this kiln door is such that it has no tendency 
to warp or twist. The framework is solid and the body 
is made of thin slats placed so that the slat on either side 

Fig. 85. An Asbestos-lined Kiln Door of the Hinge Type. 

covers the open space of the other with asbestos roofing 
fabric in between. This makes a comparatively light 
and inexpensive door, and one that absolutely holds the 
heat. These doors may be built either swinging, hoisting, 
or sliding. 

In Figure 86 will be seen the Twin Carrier type of door 
hangers with doors loaded and rolling clear of the opening. 





n . m nm 

r^ M-J ' ' ' 'I' ' " * I I I I I 




Fig. 86. Twin Carrier with Kiln Door loaded and rolling clear of Opening. 


n ! I n 







I mi I 

Fie. 87. Twin Carriers for Kiln Doors 18 to 35 Feet wide. 



In Figure 87 will be seen the Twin Carrier for doors 18 
to 35 feet wide, idle on a section of the track. 

In Figure 88 will be seen another type of carrier for kiln 

In Figure 89 will be seen the preceding type of kiln door 
carrier in operation. 

In Figure 90 will be seen another type of carrier for 
kiln doors. 

In Figure 91 will be seen kiln doors seated, wood con- 
struction, showing 3 1" X 5f" inch-track timbers and 

Fig. 88. Kiln Door Carrier engaged to Door Ready for lifting. 

trusses, supported on 4-inch by 6-inch jamb posts. "T" 
rail track, top and side, inclined shelves on which the kiln 
door rests. Track timber not trussed on openings under 
12 feet wide. 

In Figure 92 will be seen kiln doors seated, fire-proof 
construction, showing 12-inch, channel, steel hntels, 2" X 2" 
steel angle mullions, track brackets bolted to the steel 
lintels and "T" rail track. No track timbers or trusses 







— •*<*»*'^r fii- 

Fig. 90. Kiln Door Construction witli Door Carrier out of Sight. 

Fig. 91. Kiln Door Construction. Doors Seated. Wood Construction. 





mIbBHB . i,,-*' ' ' 

■t* . 


1^ f 











10 20 50 40 50 60 70 60 90 100 

Fui, 93. Tlio Uoitwl States Forest Service Humidity Diagram for determination of Absolute Humiditioe. 
Dew Points and Vapor Pressures; also Relative Humidities by means of Wet and Dry-Bulb 
Thermometer, for any temperatures and change in temperature. 


helpful appliais^ces i^ 

The Humidity Diagram 

Some simple means of determining humidities and 
changes in humidity brought about by changes in tem- 
perature in the dry kiln without the use of tables is almost 
a necessity. To meet this requirement the United States 
Forestry Service has devised the Humidity Diagram shown 
in Figure 93. It differs in several respects from the hy- 
drodeiks now in use. 

The purpose of the humidity diagram is to enable the 
dry-kiln operator to determine quickly the humidity con- 
ditions and vapor pressure, as well as the changes which 
take place with changes of temperature. The diagram 
above is adapted to the direct solution of problems of 
this character without recourse to tables or mathematical 

The humidity diagram consists of two distinct sets of 
curves on the same sheet. One set, the convex curves, 
is for the determination of relative humidity of wet-and- 
dry-bulb hygrometer or psychrometer; the other, the con- 
cave curves, is derived from the vapor pressures and shows 
the amount of moisture per cubic foot at relative humidi- 
ties and temperatures when read at the dew-point. The 
latter curves, therefore, are independent of all variables 
affecting the wet-bulb readings. They are proportional 
to vapor pressures, not to density, and, therefore, may be 
followed from one temperature to another with correctness. 
The short dashes show the correction (increase or decrease) 
which is necessary in the relative humidity, read from the 
convex curves, with an increase or decrease from the normal 
barometric pressure of 30 inches, for which the curves 


have been plotted. This correction, except for very low 
temperatures, is so small that it may usually be disregarded. 
The ordinates, or vertical distances, are relative hu- 
midity expressed in per cent of saturation, from per cent 
at the bottom to 100 per cent at the top. The abscissae, or 
horizontal distances, are temperatures in degrees Fahrenheit 
from 30 degrees below zero, at the left, to 220 degrees above, 
at the right. 

Examples of Use 

The application of the humidity diagram can best be 
understood by sample problems. These problems also 
show the wide range of conditions to which the diagram 
will apply. 

Example 1. To find the relative humidity by use of wet- 
and-dry-bulb hygrometer or psychrometer : 

Place the instrument in a strong circulation of air, or 
wave it to and fro. Read the temperature of the dry bulb 
and the wet, and subtract. Find on the horizontal line 
the temperature shown by the dry-bulb thermometer. 
Follow the vertical line from this point till it intersects 
with the convex curve marked with the difference between 
the wet and dry readings. The horizontal line passing 
through this intersection will give the relative humidity. 

Example: Dry bulb 70°, wet bulb 62°, difference 8°. 
Find 70° on the horizontal line of temperature. Follow 
up the vertical line from 70° until it intersects with the 
convex curve marked 8°. The horizontal Hne passing 
through this intersection shows the relative humidity to be 
64 per cent. 
Example 2. To find how much water per cubic foot is con- 
tained in the air: 

Find the relative humidity as in example 1. Then the 
nearest concave curve gives the weight of water in grains 
per cubic foot when the air is cooled to the dew-point. 
Using the same quantities as in example 1, this will be 
slightly more than 5 grains. 
Example 3. To find the amount of water required to saturate 
air at a given temperature: 

Find on the top line (100 per cent humidity) the given 
temperature; the concave curve intersecting at or near 


this point gives the number of grains per cubic foot. 
(Interpolate, if great accuracy is desired.) 

Example 4. To find the dew-point: 

Obtain the relative humidity as in example 1. Then 
follow up parallel to the nearest concave curve until the 
top horizontal (indicating 100 per cent relative humidity) 
is reached. The temperature on this horizonal hne at 
the point reached will be the dew-point. 

Example: Dry bulb 70°, wet bulb 62°. On the verti- 
cal line for 70° find the intersection with the hygrometer 
(convex) curve for 8°. This will be found at nearly 64 per 
cent relative humidity. Then follow up parallel with the 
vapor pressure (concave) curve marked 5 grains to its 
intersection at the top of the chart with the 100 per cent 
humidity line. This gives the dew-point as 57°. 

Example 5. To find the change in the relative humidity pro- 
duced by a change in temperature: 

Example: The air at 70° Fahr. is found to contain 64 
per cent humidity; what will be its relative humidity if 
heated to 150° Fahr.? Starting from the intersection of 
the designated humidity and temperature coordinates, 
follow the vapor-pressure curve (concave) until it inter- 
sects the 150° temperature ordinate. The horizontal line 
then reads 6 per cent relative humidity. The same opera- 
tion applies to reductions in temperature. In the above 
example what is the humidity at 60°? Following parallel to 
the same curve in the opposite direction until it intersects 
the 60° ordinate gives 90 per cent; at 57° it becomes 100 
per cent, reaching the dew-point. 

Example 6. To find the amount of condensation produced by 
lowering the temperature: 

Example: At 150° the wet bulb reads 132°. How much 
water would be condensed if the temperature were lowered 
to 70°? The intersection of the hygrometer curve for 18° 
(150°-132°) with temperature line for 150° shows a rela- 
tive humidity of 60 per cent. The vapor-pressure curve 
(concave) followed up to the 100 per cent relative humidity 
line shows 45 grains per cubic foot at the dew-point, which 
corresponds to a temperature of 130°. At 70° it is seen 
that the air can contain but 8 grains per cubic foot (satura- 
tion). Consequently, there will be condensed 45 minus 8, or 
37 grains per cubic foot of space measured at the dew-point. 



Example 7. To find the amount of water required to produce 
saturation by a given rise in temperature: 

Example: Take the values given in example 5. The air 
at the dew-point contains slightly over 5 grains per cubic 
foot. At 150° it is capable of containing 73 grains per 
cubic foot. Consequently, 73-5 = 68 grains of water 
which can be evaporated per cubic foot of space at the 
dew-point when the temperature is raised to 150°. But 
the latent heat necessary to produce evaporation must be 
supplied in addition to the heat required to raise the air 
to 150°. 

Example 8. To find the amount of water evaporated during 
a given change of temperature and humidity: 

Example: At 70° suppose the humidity is found to be 
64 per cent and at 150° it is found to be 60 per cent. How 
much water has been evaporated per cubic foot of space? 
At 70° temperature and 64 per cent humidity there are 
5 grains of water present per cubic foot at the dew-point 
(example 2). At 150° and 60 per cent humidity there are 
45 grains present. Therefore, 45-5=40 grains of water 
which have been evaporated per cubic foot of space, 
figuring all volumes at the dew-point. 

Example 9. To correct readings of the hygrometer for changes 
in barometric pressure: 

A change of pressure affects the reading of the wet bulb. 
The chart applies at a barometric pressure of 30 inches, 
and, except for great accuracy, no correction is generally 

Find the relative humidity as usual. Then look for the 
nearest barometer line (indicated by dashes). At the end 
of each barometer line will be found a fraction which repre- 
sents the proportion of the relative humidity already found, 
which must be added or subtracted for a change in baro- 
metric pressure. If the barometer reading is less than 
30 inches, add; if greater than 30 inches, subtract. The 
figures given are for a change of 1 inch; for other changes 
use proportional amounts. Thus, for a change of 2 inches 
use twice the indicated ratio; for half an inch use half, 
and so on. 

Example: Dry bulb 67°, wet bulb 51°, barometer 28 
inches. The relative humidity is found, by the method 
given in example 1, to equal 30 per cent. The barometric 


line gives a value of 3/lOOH for each inch of change. 

Since the barometer is 2 inches below 30, multiply 
3/lOOH by 2, giving 6/lOOH. The correction will, there- 
fore, be 6/100 of 30, which equals 1.8. Since the barometer 
is below 30, this is to be added, giving a corrected relative 
humidity of 31.8 per cent. 

This has nothing to do with the vapor pressure (concave) 
curves, which are independent of barometric pressure, and 
consequently does not affect the solution of the previous 

Example 10. At what temperature must the condenser be 
maintained to produce a given humidity? 

Example: Suppose the temperature in the drying room 
is to be kept at 150° Fahr., and a humidity of 80 per cent 
is desired. If the humidity is in excess of 80 per cent the 
air must be cooled to the dew-point corresponding to this 
condition (see example 4), which in this case is 141.5°. 

Hence, if the condenser cools the air to this dew point 
the required "condition is obtained when the air is again 
heated to the initial temperature. 

Example 11. Determination of relative humidity by the dew- 
point : 

The quantity of moisture present and relative humidity 
for any given temperature may be determined directly 
and accurately by finding the dew-point and applying the 
concave (vapor-pressure) curves. This does away with 
the necessity for the empirical convex curves and wet- 
and-dry-bulb readings. To find the dew-point some form 
of apparatus, consisting essentially of a thin glass vessel 
containing a thermometer and a volatile liquid, such as 
ether, may be used. The vessel is gradually cooled through 
the evaporation of the liquid, accelerated by forcing air 
through a tube until a haze or dimness, due to condensa- 
tion from the surrounding air, first appears upon the brighter 
outer surface of the glass. The temperature at which the 
haze first appears is the dew-point. Several trials should 
be made for this temperature determination, using the 
average temperature at which the haze appears and 

To determine the relative humidity of the surrounding 
air by means of the dew-point thus determined, find the 
concave curve intersecting the top horizontal (100 per 


cent relative humidity) line nearest the dew-point tem- 
perature. Follow parallel with this curve till it intersects 
the vertical line representing the temperature of the sur- 
rounding air. The horizontal line passing through this 
intersection will give the relative humidity. 

Example: Temperature of surrounding air is 80; dew- 
point is 61; relative humidity is 53 per cent. 

The dew-point determination is, however, not as con- 
venient to make as the wet-and-dry-bulb hygrometer 
readings. Therefore, the hygrometer (convex) curves are 
ordinarily more useful in determining relative humidities. 

The Hygrodeik 

In Figure 94 will be seen the Hygrodeik. This instru- 
ment is used to determine the amount of moisture in the 
atmosphere. It is a very useful instrument, as the readings 
may be taken direct with accuracy. 

To find the relative humidity in the atmosphere, swing 
the index hand to the left of the chart, and adjust the 
sliding pointer to that degree of the wet-bulb thermometer 
scale at which the mercury stands. Then swing the index 
hand to the right until the sliding pointer intersects the 
curved line, which extends downwards to the left from 
the degree of the dry-bulb thermometer scale, indicated 
by the top of the mercury column in the dry-bulb tube. 

At that intersection, the index hand will point to the 
relative humidity on scale at bottom of chart (for example 
see Fig. 94). Should the temperature indicated by the 
wet-bulb thermometer be 60 degrees, and that of the dry- 
bulb 70 degrees, the index hand will indicate humidity 
55 degrees, when the pointer rests on the intersecting 
line of 60 degrees and 80 degrees. 

The Recording Hygrometer 

In Figure 95 is shown the Recording Hygrometer com- 
plete with wet and dry bulbs, two connecting tubes and 
two recording pens and special moistening device for 
supplying water to the wet bulb. 

This equipment is designed particularly for use in con- 
nection with dry rooms and dry kilns and is arranged so 


that the recording instrument and the water supply bottle 
may be installed outside of the dry kiln or drying room, 
while the wet and dry bulbs are both installed inside the 

Fig. 94. The Hygrodeik. 

room or kiln at the point where it is desired to measure 
the humidity. This instrument records on a weekly 
chart the humidity for each hour of the day, during the 
entire week. 



The Registering Hygrometer 

In Figure 96 is shown the Registering Hygrometer, 
which consists of two especially constructed thermometers. 
The special feature of the thermometers permits placing 

Fig. 95. The Recording Hygrometer, Coraplete with Wet and Dry Bulbs. 
This instrument records on a weekly chart the humidity for each 
hour of the day, during the entire week. 

the instrument in the dry kiln without entering the drying 
room, through a small opening, where it is left for about 
20 minutes. 

The temperature of both the dry and wet bulbs are 
automatically recorded, and the outside temperature will 
not affect the thermometers when removed from the kiln. 
From these recorded temperatures, as shown when the 
instrument is removed from the kiln, the humidity can 
be easily determined from a simple form of chart which 
is furnished free by the makers with each instrument. 


The Recording Thermometer 

In Figure 97 is shown the Recording Thermometer for 
observing and recording the temperatures within a dry 
kiln, and thus obtaining a check upon its operation. This 

Fig. 96. The Registering Hygrometer. 

Fig. 97. The Recording Thermometer. 



instrument is constructed to record automatically, upon 
a circular chart, the temperatures prevailing within the 
drying room at all times of the day and night, and serves 
not only as a means of keeping an accurate record of the 
operation of the dry kiln, but as a valuable check upon 

the attendant in charge of the drying 


The Registering Thermometer 

In Figure 98 is shown the Register- 
ing Thermometer, which is a less ex- 
pensive instrument than that shown 
in Figure 97, but by its use the maxi- 

Fig. 98. The Registering 

Fig. 99. The Recording Steam- 
Pressure Gauge. 

mum and minimum temperatures in the drying room 
during a given period can be determined. 

The Recording Steam Gauge 

In Figure 99 is shown the Recording Steam Pressure 
Gauge, which is used for accurately recording the steam 
pressures kept in the boilers. This instrument may be 


mounted near the boilers, or may be located at any dis- 
tance necessary, giving a true and accurate record of the 
fluctuations of the steam pressure that may take place 
within the boilers, and is a check upon both the day and 
night boiler firemen. 

The Troemroid Scalometer 

In Figure 100 is shown the Troemroid Scalometer. This 
instrument is a special scale of extreme accuracy, fitted 

Fig. 100. The Troemroid Scalometer. 

with agate bearings with screw adjustment for balancing. 
The beam is graduated from to 2 ounces, divided into 
100 parts, each division representing l-50th of an ounce; 
and by using the pointer attached to the beam weight, 
the 1-lOOth part of an ounce can be weighed. 

The percentage table No. II has a range from one half 
of 1 per cent to 30 per cent and is designed for use where 
extremely fine results are needed, or where a very small 


amount of moisture is present. Table No. Ill ranges 
from 30 per cent up to 90 per cent. These instruments 
are in three models as described below. 

Model A. (One cylinder) ranges, from ^ of 1 per cent to 30 
per cent and is to be used for testing moisture contents 
in kiln-dried and air-dried lumber. 

Model B. (Two cylinders) ranges from ^ of 1 per cent up to 
90 per cent and is to be used for testing the moisture 
contents of kiln-dried, air-dried, and green lumber. 

Model C. (One cylinder) ranges from 30 per cent to 90 per 
cent and is applicable to green lumber only. 

Test Samples. — The green boards and all other boards 
intended for testing should be selected from boards of fair 
average quality. If air-dried, select one about half way 
up the height of the pile of lumber. If kiln-dried, two 
thirds the height of the kiln car. Do not remove the kiln 
car from the kiln until after the test. Three of four test 
pieces should be cut from near the middle of the cross- 
wise section of the board, and | to fV inch thick. Re- 
move the superfluous sawdust and splinters. When the 
test pieces are placed on the scale pan, be sure their weight 
is less than two ounces and more than If ounces. If 
necessary, use two or more broken pieces. It is better if 
the test pieces can be cut off on a fine band saw. 

Weighing. — Set the base of the scale on a level surface 
and accurately balance the scale beam. Put the test 
pieces on the scale pan and note their weight on the lower 
edge of the beam. Set the indicator point on the hori- 
zontal bar at a number corresponding to this weight, which 
may be found on the cylinder at the top of the table. 

Dry the test pieces on the Electric Heater (Fig. 101) 
30 to 40 minutes, or on the engine cylinder two or three 
hours. Weigh them at once and note the weight. Then 
turn the cylinder up and at the left of it under the small 
pointer find the number corresponding to this weight. 
The percentage of moisture lost is found directly under 
pointer on the horizontal bar first mentioned. The lower 
portion on the cylinder Table No. II is an extension of 


the upper portion, and is manipulated in the same manner 
except that the bottom hne of figures is used for the 
first weight, and the right side of cyhnder for second weight. 
Turn the cyhnder down instead of up when using it. 

Examples (Test Pieces) 

Model A. Table No. II, Kiln-dried or Air-dried Lumber: 
If first weight is 90^ and the second weight is 87, the cylinder 
table will show the board from which the test pieces were 
taken had a moisture content of 3.8 per cent. 

Model B. Tables No. II and III, Air-dried (also Green and 
KUn-dried) Lumber. 

If the first weight on lower cylinder is 97 and the second 
weight is 76, the table will show 21.6 per cent of moisture. 

Model C. Table III, Green Lumber: 

If the first weight is 94 and the second weight is 51, the 
table shows 45.8 per cent of moisture. 

Keep Records of the Moisture Content 

Saw Mills. — Should test and mark each pile of lumber 
when first piled in the yard, and later when sold it should 
be again tested and the two records given to the purchaser. 

Factories. — Should test and mark the lumber when 
first received, and if piled in the yard to be kiln-dried 
later, it should be tested before going into the dry kiln, 
and again before being removed, and these records placed 
on file for future reference. 

Kiln-dried lumber piled in storage rooms (without any 
heat) will absorb 7 to 9 per cent of moisture, and even 
when so stored should be tested for moisture before being 
manufactured into the finished product. 

Never work lumber through the factory that has more 
than 5 or 6 per cent of moisture or less than 3 per cent. 

Dry storage rooms should be provided with heating 
coils and properly ventilated. 

Oak or any other species of wood that shows 25 or 30 
per cent of moisture when going into the dry kiln, will 
take longer to dry than it would if it contained 15 to 20 
per cent, therefore the importance of testing before putting 
into the kiln as well as when taking it out. 



The Electric Heater 

In Figure 101 is shown the Electric Heater. This 
heater is especially designed to dry quickly the tect pieces 
for use in connection with the Scalometer (see Fig. 100) 
without charring them. It may be attached to any electric 

Fig. 101. The Electric Heater. 

light socket of 110 volts direct or alternating current. A 
metal rack is provided to hold the test pieces vertically 
on edge. 

Turn the test pieces over once or twice while drying. 

It will require from 20 minutes to one hour to remove 
all the moisture from the test pieces when placed on this 
heater, depending on whether they are cut from green, 
air-dried, or kiln-dried boards. 

Test pieces cut from softwoods will dry quicker than 
those cut from hardwoods. 

When the test pieces fail to show any further loss in 
weight, they are then free from all moisture content. 


American Blower Company, Detroit, Mich. 

Imre, James E., "The Kiln-drying of Gum," The United States 
Dept. of Agriculture, Division of Forestry. 

National Dry Kiln Company, Indianapolis, Ind. 

Prichard, Reuben P., ''The Structure of the Common Woods," 
The United States Dept. of Agriculture, Division of For- 
estry, Bulletin No. 3. 

Roth, Filibert, "Timber," The United States Dept. of Agri- 
culture, Division of Forestry, Bulletin No. 10. 

Standard Dry Kiln Company, Indianapolis, Ind. 

Sturtevant Company, B. F., Boston, Mass. 

TiEMAN, H, D., "The Effects of Moisture upon the Strength and 
Stiffness of Wood," The United States Dept. of Agricul- 
ture, Division of Forestry, Bulletin No. 70. 

TiEMAN, H, D., "Principles of Kiln-drying Lumber," The United 
States Dept. of Agriculture, Division of Forestry. 

TiEMAN, H. D., " The Theory of Drying and its Application, etc.," 
The United States Dept. of Agriculture, Division of 
Forestry, Bulletin No. 509. 

The United States Dept. of Agriculture, Division of For- 
estry, "Check List of the Forest Trees of the United 

The United States Dept. of Agriculture, Division of 
Forestry, Bulletin No. 37. 

Von Schrenk, Herman, "Seasoning of Timbers," The United 
States Dept. of Agriculture, Division of Forestry, Bul- 
letin No. 4L 

Wagner, J. B., "Cooperage," 1910. 


Abnormal. Differing from the usual structure. 

Acuminate. Tapering at the end. 

Adhesion. The union of members of different floral whorls. 

Air-seasoning. The drying of wood in the open air. 

Albumen. A name applied to the food store laid up outside the 

embryo in many seeds; also nitrogenous organic matter 

found in plants. 
Albumam. Sapwood. 
Angiosperms. Those plants which bear their seeds within a 

Annual rings. The layers of wood which are added annually to 

the tree. 
Apartment kiln. A drying arrangement of one or more rooms 

with openings at each end. 
Arborescent. A tree in size and habit of growth. 

Baffle plate. An obstruction to deflect air or other currents. 

Bastard cut. Tangential cut. Wood of inferior cut. 

Berry. A fruit whose entire pericarp is succulent. 

Blower kiln. A drying arrangement in which the air is blown 

through heating coils into the drying room. 
Box kiln. A small square heating room with openings in one end 

Brittleness. Aptness to break; not tough; fragility. 
Burrow. A shelter; insect's hole in the wood. 

Calorie. Unit of heat; amount of heat which raises the 

Caljrx. The outer whorl of floral envelopes. 
Capillary. A tube or vessel extremely fine or minute. 
Case-harden. A condition in which the pores of the wood are 

closed and the outer surface dry, while the inner portion is 

still wet or unseasoned. 
Cavity. A hollow place; a hollow. 
Cell. One of the minute, elementary structures comprising the 

greater part of plant tissue. 
Cellulose. A primary cell-wall substance. 


Checks. The small chinks or cracks caused by the rupture of the 

wood fibres. 
Cleft. Opening made by spHtting; divided. 
Coarse-grained. Wood is coarse-grained when the annual rings 

are wide or far apart. 
Cohesion. The union of members of the same floral whorl. 
Contorted. Twisted together. 
Corolla. The inner whorl of floral envelopes. 
Cotyledon. One of the parts of the embryo performing in part the 

function of a leaf, but usually serving as a storehouse of food 

for the developing plant. 
Crossers. Narrow wooden strips used to separate the material on 

kiln cars. 
Cross-grained. Wood is cross-grained when its fibres are spiral 

or twisted. 

Dapple. An exaggerated form of mottle. 

Deciduous. Not persistent; applied to leaves that fall in autumn 
and to calyx and corolla when they fall of! before the fruit 

Definite. Limited or defined. 

Dew-point. The point at which water is deposited from moisture- 
laden air. 

Dicotyledon. A plant whose embryo has two opposite cotyledons. 

Diffuse. Widely spreading. 

Disk. A circular, flat, thin piece or section of the tree. 

Duramen. Heartwood. 

Embryo. Applied in botany to the tiny plant within the seed. 
Enchinate. Beset with prickles. 

Expansion. An enlargement across the grain or lengthwise of the 

Fibres. The thread-hke portion of the tissue of wood. 

Fibre-saturation point. The amount of moisture wood will im- 
bibe, usually 25 to 30 per cent of its dry-wood weight. 

Figure. The broad and deep medullary rays as in oak showing 
when the timber is cut into boards. 

Filament. The stalk which supports the anther. 

Fine-grained. Wood is fine-grained when the annual rings are 
close together or narrow. 

Germination. The sprouting of a seed. 

Girdling. To make a groove around and through the bark of a 
tree, thus killing it. 


Glands. A secreting surface or structure; a protuberance having 

the appearance of such an organ. 
Glaucous. Covered or whitened with a bloom. 
Grain. Direction or arrangement of the fibres in wood. 
Grubs. The larvae of wood-destroying insects. 
G3rmnosperms. Plants bearing naked seeds; without an ovary. 

Habitat. The geographical range of a plant. 

Heartwood. The central portion of tree. 

Hollow-homing. Internal checking. 

Honey-combing. Internal checking. 

Hot-blast kiln. A drying arrangement in which the air is blown 

through heating coils into the drying room. 
Humidity. Damp, moist. 
Hygroscopicity. The property of readily imbibing moisture from 

the atmosphere. 

Indefinite. Applied to petals or other organs when too numerous 

to be conveniently counted. 
Indigenous. Native to the country. 
Involute. A form of vernation in which the leaf is rolled inward 

from its edges. 

Kiln-drying. Drying or seasoning of wood by artificial heat in an 
inclosed room. 

Leaflet. A single division of a compound leaf. 

Limb. The spreading portion of the tree. 

Lumen. Internal space in the spring- and summer-wood fibres. 

Median. Situated in the middle. 

Medulla. The pith. 

Medullary rays. Rays of fundamental tissue which connect the 

pith with the bark. 
Membranous. Thin and rather soft, more or less translucent. 
Midrib. The central or main rib of a leaf. 
Moist-air kiln. A drying arrangement in which the heat is taken 

from radiating coils located inside the drying room. 
Mottle. Figure transverse of the fibres, probably caused by the 

action of wind upon the tree. 

Non-porous. Without pores. 

Oblong, Considerably longer than broad, with flowing outline. 
Obtuse. Blunt, rounded. 

256 ^^^ GLOSSARY 

Oval. Broadly elliptical. 

Ovary. The part of the pistil that contains the ovules. 

Parted. Cleft nearly, but not quite to the base or midrib. 
Parench3rma. Short cells constituting the pith and pulp of the 

Pericarp. The walls of the ripened ovary, the part of the fruit 

that encloses the seeds. 
Permeable. Capable of being penetrated. 
Petal. One of the leaves of the corolla. 

Pinholes. Small holes in the wood caused by worms or insects. 
Pistil. The modified leaf or leaves which bear the ovules; usually 

consisting of ovary, style and stigma. 
Plastic. Elastic, easily bent. 
Pocket kilns. Small drying rooms with openings on one end only 

and in which the material to be dried is piled directly on the 

Pollen. The fertilizing powder produced by the anther. 
Pores. Minute orifices in wood. 
Porous. Containing pores. 
Preliminary steaming. Subjecting wood to a steaming process 

before drying or seasoning. 
Progressive kiln. A drying arrangement with openings at both 

ends, and in which the material enters at one end and is dis- 
charged at the other. 

Rick. A pile or stack of lumber. 

Rift. To split; cleft. 

Ring shake. A large check or crack in the wood following an 

annual ring. 
Roe. A peculiar figure caused by the contortion of the woody 

fibres, and takes a wavy line parallel to them. 

Sapwood. The outer portions of the tree next to the bark; 

Saturate. To cause to become completely penetrated or soaked. 
Season checks. Small openings in the ends of the wood caused 

by the process of drying. 
Seasoning. The process by which wood is dried or seasoned. 
Seedholes. Minute holes in wood caused by wood-destroying 

worms or insects. 
Shake. A large check or crack in wood caused by the action of 

the wind on the tree. 
Shrinkage. A lessening or contraction of the wood substance. 


Skidways. Material set on an incline for transporting lumber or 

Species. In science, a group of existing things, associated accord- 
ing to properties. 

Spermatophyta. Seed-bearing plants. 

Spring-wood. Wood that is formed in the spring of the year. 

Stamen. The pollen-bearing organ of the flower, usually con- 
sisting of filament and anther. 

Stigma. That part of the pistil which receives the pollen. 

Style. That part of the pistil which connects the ovary with the 

Taproot. The main root or downward continuation of the plant 

Temporary checks. Checks or cracks that subsequently close. 
Tissue. One of the elementary fibres composing wood. 
Thunder shake. A rupture of the fibres of the tree across the 

grain, which in some woods does not always break them. 
Tornado shake. (See Thunder shake.) 
Tracheids. The tissues of the tree which consist of vertical cells 

or vessels closed at one end. 

Warping. Turning or twisting out of shape. 
Wind shake. (See Thunder shake.) 

Working. The shrinking and swelhng occasioned in wood. 
Wormholes. Small holes in wood caused by wood-destroying 

Vernation. The arrangment of the leaves in the bud. 

Whorl. An arrangement of organs in a circle about a central axis. 


Abies amabalis, 21 
Abies balsamea, 20 
Abies concolor, 20 
Abies grandis, 20 
Abies magnifica, 21 
Abies nobilis, 21 
Acer macrophyllum, 69 
Acer negundo, 69 
Acer Pennsylvanicum, 70 
Acer rubrum, 69 
Acer saccharinum, 69 
Acer saccharum, 68 
Acer spicatum, 69 
iEsculus flava, 45 
^sculus glabra, 45 
JEsculus octandra, 45 
Ailanthus glandulosa, 37 
Asimina triloba, 76 

Betula lenta, 41 
Betula lutea, 42 
Betula nigra, 43 
Betula papyrifera, 43 
Betula populifolia, 42 
Betula rubra, 43 
Buxus sempervirens, 77 

Carpinus Caroliana, 44 
Castanea Americana, 48 
Castanea chrysophylla, 49 
Castanea dentata, 48 
Castanea pumila, 48 
Castanea vesca, 48 
Castanea vulgaris, 48 
Catalpa bignonioides, 46 
Catalpa speciosa, 46 
Celtis occidentalis, 62 
Chamsecyparis Lawsonia, 18 
Chamsecyparis thyoides, 17 
Cladrastis lutea, 85 
Cornus florida, 49 
Cupressus nootkatensis, 18 

Diospyros Virginia, 77 

Evonymus atropurpureus, 82 

Fagus ferruginea, 40 
Fraxinus Americana, 37 
Fraxinus Caroliniana, 39 
Fraxinus nigra, 38 
Fraxinus Oregana, 38 
Fraxinus Pennsylvanica, 38 
Fraxinus pubescens, 38 
Fraxinus quadrangulata, 38 
Fraxinus sambucifolia, 38 
Fraxinus viridis, 38 

Gleditschia triacanthos, 66 
Gymnocladus dioicus, 49 

Hicoria alba, 64 
Hicoria glabra, 64 
Hicoria minima, 64 
Hicoria ovata, 64 
Hicoria pecan, 64 

Ilex monticolo, 65 
Ilex opaca, 64 

Juglans cinerea, 45 
Juglans nigra, 82 
Juniperus communis, 19 
Juniperus Virginiana, 18 

Larix Americana, 22 
Larix laricina, 22 
Larix occidentalis, 22 
Libocedrus decurrens, 18 
Liquidamber styraciflua, 54 
Liriodendron tulipfera, 81 

Madura aurantiaca, 76 
Magnolia acuminata, 67 
Magnolia glauca, 67 



Magnolia tripetala, 67 
Morus rubra, 70 

Nyssa aquatica, 60 
Nyssa sylvatica, 62 

Ostrya Virginiana, 65 
Oxydendrum arboreum, 80 

Picea alba, 28 
Picea canadensis, 28 
Picea engelmanni, 28 
Picea mariana, 27 
Picea nigra, 27 
Picea rubens, 28 
Picea sitchensis, 28 
Pinus banksiana, 27 
Pinus cubensis, 26 
Pinus divaricata, 27 
Pinus enchinata, 26 
Pinus flexilis, 24 
Pinus inops, 27 
Pinus Jeffreyi, 25 
Pinus Lambertiana, 24 
Pinus monticolo, 24 
Pinus Murryana, 27 
Pinus palustris, 24 
Pinus ponderosa, 25 
Pinus resinosa, 25 
Pinus rigida, 26 
Pinus strobus, 23 
Pinus tseda, 25 
Pinus Virginiana, 27 
Platanus occidentalis, 80 
Platanus racemosa, 81 
Populus alba, 79 
Populus angulata, 77 
Populus balsamifera, 79 
Populus fremontii, 78 
Populus grandidentata, 79 
Populus heteropylla, 78 
Populus monilifera, 77 
Populus nigra italica, 79 
Populus tremuloides, 79 
Populus trichocarpa, 78 
Populus Wislizeni, 78 
Prunus Pennsylvanica, 47 
Prunus serotina, 47 
Pseudotsuga douglasii, 29 
Pseudotsuga taxifolia, 29 
Pyrus coronaria, 49 

Quercus acuminata, 73 
Quercus alba, 71 


aquatica, 73 
bicolor, 72 
chrysolepis, 76 
coccinea, 75 
digitata, 75 
durandii, 71 
falcata, 75 
garryana, 71 
ilicijolia, 74 
imbricaria, 75 
lobata, 72 
lyrata, 73 
macrocarpa, 72 
marilandica, 75 
Michauxii, 74 
minor, 74 
nigra, 75 
obtusiloda, 74 
palustris, 73 
phellos, 72 
platanoides, 72 
prinoides, 74 
prinus, 73 
pumila, 74 
rubra, 74 
tinctoria, 74 
velutina, 74 
virens, 75 

Rhamnus Caroliniana, 45 
Robinia pseudacacia, 66 
Robinia viscosa, 66 

Salix alba, 83 
Salix amygdaloides, 84 
Salix babylonica, 84 
Salix bebbiana, 84 
Salix discolor, 84 
Salix fluviatilis, 84 
Salix fragilis, 84 
Salix lucida, 84 
Salix nigra, 83 
Salix rostrata, 84 
Salix vitellina, 83 
Sassafras sassafras, 80 
Sequoia sempervirens, 19 

Taxodium distinchum, 19 
Taxus brevifolia, 30 
Thuya gigantea, 17 
Thuya occidentalis, 17 
Tilia Americana, 39 
TiUa heterophylla, 39 


Tilia pubescens, 39 Ulmus crassifolia, 51 

Tsuga canadensis, 21 Ulmus fulva, 51 

Tsuga mertensiana, 21 Ulmus pubescens, 51 

Ulmus racemosa, 50 

Ulmus alata, 51 Umbellularia Calif ornica, 65 
Ulmus Americana, 50 


Abelb, Tree, 79 

Absorption of water by dry wood, 124 

Acacia, 66 

Acacia, false, 66 

Acacia, three-thorned, 66 

According to species, different kiln 
drying, 170 

Advantages in seasoning, 128 

Advantages of kiln-drying over air- 
drying, 156 

Affect drying, properties of wood 
that, 156 

Ailanthus, 37 

Air circulation, 173 

Air-drying, advantages of kiln-dry- 
ing over, 156 

Alaska cedar, 18 

Alaska cypress, 18 

Alcoholic liquids, stave and heads of 
barrels containing, 112 

Almondleaf willow, 84 

Ambrosia or timber beetles, 99 

American box, 49 

American elm, 50 

American larch, 22 

American linden, 39 

American oak, 71 

American red pine, 25 

Anatomical structure, 14 

Annual ring, the yearly or, 10 

Apartment dry kiln, 198 

Apple, crab, 49 

Apple, custard, 76 

Apple, wild, 49 

Appliances in kiln-drying, helpful, 237 

Arborvitse, 17 

Ash, 37 

Ash, black, 38 

Ash, blue, 38 

Ash, Carolina, 39 

Ash, green, 38 

Ash, ground, 38 

Ash, hoop, 38 

Ash-leaved maple, 69 

Ash, Oregon, 38 

Ash, red, 38 

Ash, white, 37 

Aspen, 39, 79 

Aspen, large-toothed, 78 

Aspen-leaved birch, 42 

Aspen, quaking, 79 

Atmospheric pressure, drying at, 146 

Bald Cypress, 19 

Ball tree, button, 80 

Balm of gilead, 79 

Balm of gilead fir, 20 

Balsam, 20, 79 

Balsam fir, 20 

Bark and pith, 8 

Bark on, round timber with, 106 

Barrels containing alcoholic liquids, 

staves and heads of, 112 
Barren oak, 75 
Bar willow, sand, 84 
Basket oak, 74 
Basswood, 39 

Basswood, small-leaved, 39 
Basswood, white, 39 
Bastard pine, 26 
Bastard spruce, 29 
Bay poplar, 60 
Bay, sweet, 67 
Bear oak, 74 
Beaver wood, 67 
Bebb willow, 84 
Bee tree, 39 
Beech, 40 
Beech, blue, 44 
Beech, red, 40 
Beech, water, 44, 80 
Beech, white, 40 
Berry, sugar, 62 
Beetles, ambrosia or timber, 99 



Big bud hickory, 64 

Bilsted, 54 

Birch, 41 

Birch, aspen-leaved, 42 

Birch, black, 41 

Birch, canoe, 43 

Birch, cherry, 41 

Birch, gray, 42 

Birch, mahogany, 41 

Birch, old field, 42 

Birch, paper, 43 

Birch, red, 42 

Birch, river, 43 

Birch, silver, 42 

Birch, sweet, 41 

Birch, white, 42, 43 

Birch, wintergreen, 41 

Birch, yellow, 42 

Bird cherry, 47 

Bitternut hickory, 64 

Black ash, 38 

Black birch, 41 

Black cherry, 47 

Black Cottonwood, 78 

Black cj^ress, 19 

Black gum, 62 

Black hickory, 64 

Black jack, 75 

Black larch, 22 

Black locust, 66 

Black nut hickory, 64 

Black oak, 74 

Black pine, 25, 27 

Black spruce, 27 

Black walnut, 44, 82 

Black willow, 83 

Blower dry kiln, operation of, 186 

Blower or hot blast dry kiln, 185 

Blue ash, 38 

Blue beech, 44 

Blue poplar, 81 

Blue willow, 83 

Bois d'arc, 45, 76 

Bolts, stave, heading and shingle, 

Borers, flat-headed, 103 
Borers, powder post, 105 
Borers, round-headed, 101 
Box, American, 49 
Box elder, 69 
Box dry kiln, 204 
Broad-leaved maple, 69 
Broad-leaved trees, 31 

Broad-leaved trees, list of most im- 
portant, 37 
Broad- leaved trees, wood of, 31 
Brown hickory, 64 
Brown locust, 66 
Buckeye, 45 
Buckeye, fetid, 45 
Buckeye, Ohio, 45 
Buckeye, sweet, 45 
Buckthorne, 45 
Bud hickory, big, 64 
Bull nut hickory, 64 
Bull pine, 25 
Bur oak, 72 
Burning bush, 82 
Bush, burning, 82 
Bush, juniper, 18 
Butternut, 45 
Button ball tree, 80 
Button wood, 80 

California Redwood, 19 

California white pine, 25 

Canadian pine, 25 

Canary wood, 81 

Canoe birch, 43 

Canoe cedar, 17 

Carolina ash, 39 

Carolina pine, 26 

Carolina poplar, 77 

Cars, method of loading kiln, 206 

Catalpa, 46 

Cedar, 17 

Cedar, Alaska, 18 

Cedar, canoe, 17 

Cedar, elm, 51 

Cedar, ground, 19 

Cedar, incense, 18 

Cedar of the West, red, 17 

Cedar, Oregon, 18 

Cedar, pencil, 18 

Cedar, Port Orford, 18 

Cedar, red, 18, 19 

Cedar, white, 17, 18 

Cedar, yellow, 18 

Changes rendering drying difficult, 

Characteristics and properties of 

wood, 1 
Checking and splitting, prevention 

of, 129 
Cherry, 47 
Cherry birch, 41 



Cherry, bird, 47 

Cherry, black, 47 

Cherry, Indian, 45 

Cherry, red, 47 

Cherry, rum, 47 

Cherry, wild, 47 

Cherry, wild red, 47 

Chestnut, 48 

Chestnut, horse, 45, 65 

Chestnut oak, 73 

Chestnut oak, rock, 73 

Chestnut oak, scrub, 74 

Chinquapin, 48, 49 

Chinquapin oak, 73, 74 

Chinquapin oak, dwarf, 74 

Choice of drying method, 195 

Circassian walnut, 60 

Circulation, air, 173 

Clammy locust, 66 

Classes of trees, 5 

Cliff elm, 50 

Coast redwood, 19 

Coffee nut, 49 

Coffee tree, 49 

Color and odor of wood, 89 

Color, odor, weight, and figure in 
wood, grain, 86 

Composition of sap, 116 

Conditions and species, tempera- 
ture depends on, 171 

Conditions favorable for insect in- 
jury, 106 

Conditions governing the drying of 
wood, 156 

Conditions of success in kiln-drying, 

Coniferous trees, 8 

Coniferous trees, wood of, 8 

Coniferous woods, Ust of important, 

Containing alcoholic liquids, staves 
and heads of barrels, 112 

Cooperage stock and wooden truss 
hoops, dry, 112 

Cork elm, 50 

Cotton gum, 60 

Cottonwood, 49, 77, 78 

Cottonwood, black, 78 

Cottonwood, swamp, 78 

Cow oak, 74 

Crab apple, 49 

Crab, fragrant, 349 

Crack willow, 84 

Crude products, 106 
Cuban pine, 26 
Cucumber tree, 49, 67 
Cup oak, mossy, 72 
Cup oak, over-, 72, 73 
Custard apple, 76 
Cypress, 19 
Cypress, Alaska, 18 
Cypress, bald, 19 
Cypress, black, 19 
Cypress, Lawson's, 18 
Cypress, pecky, 19 
Cypress, red, 19 
Cypress, white, 19 

D'Arc, Bois, 45, 76 

Deal, yellow, 23 

Demands upon soil and moisture of 
red gum, 56 

Depends on conditions and species, 
temperature, 171 

Description of the forest service 
kiln, theory and, 161 

Diagram, the uses of the humidity, 237 

Difference between seasoned and 
unseasoned wood, 121 

Different grains of wood, 86 

Different kiln-drying according to 
species, 170 

Different species, weight of kiln- 
dried wood of, 95 

Different types, kilns of, 196 

Different tj^es of dry kilns, 185 

Different types of kiln doors, 231 

Difficult, changes rendering drying, 

Difficulties of drying wood, 138 

Distribution of water in wood, 114 

Distribution of water in wood, local, 

Distribution of water in wood sea- 
sonal, 115 

Dogwood, 49 

Doors, different types of kiln, 231 

Douglas spruce, 29 

Downy linden, 39 

Downy poplar, 78 

Dry cooperage stock and wooden 
truss hoops, 112 

Drying according to species, different 
kiln, 170 

Drying, advantages of kiln-drying 
over air, 156 



Drying at atmospheric pressure, 146 
Drying by superheated steam, 150 
Drying, conditions of success in kiln, 

Drying difficult, changes rendering, 

Drsdng gum, Idln, 180 
Drying, helpful appliances in kiln, 237 
Drying, kiln, 164, 177 
Drydng, losses due to improper kiln, 

Drjdng method, choice of, 195 
Drying, methods of kiln, 145 
Drying, objects of kUn, 168 
Drying of green red gum, kiln, 183 
Drying of wood, kiln, 156 
Drying of wood, physical conditions 

governing the, 156 
Drying, physical properties that in- 
fluence, 125 
Drying, properties of wood that 

effect, 141 
Drying, theory of kiln, 157 
Drying, underlying principles of 

kiln, 166 
Drying under pressure and vacuum, 

Drying, unsolved problems in kiln, 

Drying wood, difficulties of, 138 
Drying 100 lb of green wood in the 

kiln, pounds of water lost, 179 
Dry kiln, apartment, 198 
Dry kiln, box, 204 
Dry kiln, operation of the blower, 

Dry kiln, operation of the moist-air, 

Dry kiln, moist-air or pipe, 188 
Dry kiln, pocket, 200 
Dry kiln, progressive, 196 
Dry kiln, requirements in a satis- 
factory, 160 
Dry kilns, different types of, 185 
Dry kiln specialties, 206 
Dry kilns, types of, 185 
Dry kiln, tower, 202 
Dry wood, absorption of water by, 

Duck oak, 73 
Due to improper kiln-drying, losses, 

Dwarf chinquapin oak, 74 

Effects of Moisture on Wood, 

Elder, box, 69 
Electric heater, the, 250 
Elimination of stain and mildew, 136 
Elm, 50 

Elm, American, 50 
Elm, cedar, 51 
Elm, cliff, 50 
Elm, cork, 50 
Elm, hickory, 50 
Elm, moose, 51 
Elm, red, 51 
Elm, rock, 50 
Elm, slippery, 51 
Elm, water, 50 
Elm, winged, 51 
Elm, white, 50 
Enemies of wood, 98 
Evaporation of water, manner of, 123 
Evaporation, rapidity of, 124 
Expansion of wood, 135 

Factories, Scalometbr in, 249 

False acacia, 66 

Favorable for insect injury, condi- 
tions, 106 

Fetid buckeye, 45 

Fibre saturation point in wood, 118 

Field birch, old, 42 

Field pine, old, 25, 26 

Figure in wood, 96 

Figure in wood, grain, color, odor, 
weight, and, 86 

Final steaming of gum, 182 

Fir, 20 

Fir, balm of gilead, 20 

Fir balsam, 20 

Fir, noble, 21 

Fir, red, 21, 29 

Fir tree, 20 

Fir, white, 20, 21 

Fir, yellow, 29 

Flat-headed borers, 103 

Forest service kiln, theory and 
description of, 161 

Form of the red gum, 55 

Fragrant crab, 49 

Gauge, the Recording Steam, 246 
Georgia pine, 24 
Gilead, balm of, 79 
Gilead fir, balm of, 20 



Ginger pine, 18 

Glaucous willow, 84 

Governing the drying of wood, 
physical conditions, 156 

Grain, color, odor, weight, and 
figure in wood, 86 

Grains of wood, different, 86 

Gray birch, 42 

Gray pine, 27 

Green ash, 38 

Green red gum, kiln-drying, 183 

Green wood in the kiln, pounds of 
water lost in drying 100 lbs., 179 

Ground ash, 38 

Ground cedar, 19 

Growth red gum, second, 59 

Gum, 52 

Gum, black, 62 

Gum, cotton, 60 

Girtn, demands upon soil and mois- 
ture of red, 56 

Gum, final steaming of, 182 

Gum, form of red, 55 

Giun, kiln-drying, 180 

Gum, kiln-drying of green red, 183 

Gum, method of piling, 180 

Gum, preliminary steaming of, 182 

Gum, range of red, 55 

Gum, range of tupelo, 61 

Gum, red, 54, 79 

Gum, reproduction of red, 57 

Gum, second-growth red, 59 

Gum, sour, 62, 80 

Gum, sweet, 54, 80 

Gum, tolerance of the red, 56 

Gmn, tupelo, 60 

Gum, uses of tupelo, 61 

Hackberry, 62 
Hacmatac, 22 
Hard maple, 68 
Hard pine, 26 
Hard pines, 24 
Hard pine, southern, 24 
Hardwoods, 37 
Hazel pine, 54, 60 
Headed borers, flat, 103 
Headed borers, round, 101 
Heading, stave and shingle bolts, 109 
Heads and staves of barrels contain- 
ing alcoholic liquids, 112 
Heart hickory, white, 64 
Heartwood, sap and, 8 

Heater, the electric, 250 

Helpful apphcances in kiln-drying, 

Hemlock, 21 
Hemlock spruce, 21 
Hickory, 63 
Hickory, big bud, 64 
Hickory, bitternut, 64 
Hickory, black, 64 
Hickory, black nut, 64 
Hickory, brown, 64 
Hickory, bull nut, 64 
Hickory elm, 50 
Hickory, mockernut, 64 
Hickory, pignut, 64 
Hickory, poplar, 81 
Hickory, scalybark, 64 
Hickory, shagbark, 64 
Hickory, shellbark, 64 
Hickory, swamp, 64 
Hickory, switchbud, 64 
Hickory, white heart, 64 
Holly, 64, 65 
Holly, mountain, 65 
Honey locust, 66 
Honey shucks, 66 
Hoop ash, 38 
Hoops, dry cooperage stock and 

wooden truss, 112 
Hop hornbeam, 65 
Hornbeam, 44 
Hornbeam, hop, 65 
Horse chestnut, 45, 65 
Hot blast or blower kiln, 185 
Himiidity, 174 

Humidity diagram, uses of the, 237 
How to prevent insect injury, 107 
How wood is seasoned, 145 
Hygrodeik, the, 242 
Hygrometer, the recording, 242 
Hygrometer, the registering, 244 

Illinois Nut, 64 

Important broad-leaved trees, list 

of most, 37 
Important coniferous woods, Ust of, 

Impregnation methods, 151 
Improper kiln-drying, losses due to, 

Incense cedar, 18 
Indian bean, 46 
Indian cherry, 45 



Influence drying, physical proper- 
ties that, 125 

Injury, conditions favorable for in- 
sect, 106 

Injury from insects, how to prevent, 

Insect injury, conditions favorable 
for, 106 

Insects, how to prevent injury from, 

Iron oak, 74 

Ironwood, 44, 65 

Jack, Black, 75 
Jack oak, 75 
Jack pine, 27 
Jersey pine, 27 
Juniper, 18 
Juniper bush, 18 
Juniper, red, 18 
Juniper, savin, 18 

Keep Records op the Moisture 

Content, 249 
Kiln, apartment dry, 198 
Kiln, blower or hot blast, 185 
Kiln, box dry, 204 

Kiln cars and method of loading, 206 
Kiln doors, different types, 231 
Kiln-dried wood of different species, 

weight of, 95 
Kiln-drying, 164, 177 
Kiln-drying according to species, 

different, 170 
Kiln-drying, conditions of success in, 

Kiln-drying gum, 180 
Kiln-drying, helpful appliances in, 

Kiln-drying, losses due to improper, 

Kiln-drying, objects of, 168 
Kiln-drying of green red gum, 183 
Kiln-drying of wood, 156 
Kiln-drying of wood, 156 
Kiln-drying over air-drying, advan- 
tages of, 156 
Kiln-drying, theary of, 157 
Kiln-drying, underlying principles of, 

Kiln-drjdng, unsolved problems in, 

Kiln, operation of the blower dry, 186 

Kiln, operation of the moist-air dry, 

Kiln, pipe or moist-air dry, 188 
Kiln, pocket dry, 200 
Kiln, progressive dry, 196 
Kiln, requirements in a satisfactory 

dry, 160 
Kilns, different types of dry, 185 
Kilns of different types, 196 
Kiln specialities, dry, 206 
Kiln, theory and description of the 

forest service, 161 
Kilns, types of dry, 185 
Kiln, tower dry, 202 

Land Spruce, Tide, 28 

Larch, 22 

Larch, American, 22 

Larch, black, 22 

Larch, western, 22 

Large-toothed aspen, 79 

Laurel, 65 

Laurel oak, 75 

Lawson's cypress, 18 

Leaf pine, long-, 24 

Leaf pine, short-, 26 

Leaf willow, long, 84 

Leaved basswood, small, 39 

Leaved birch, aspen, 42 

Leaved maple, ash, 69 

Leaved maple, broad, 69 

Leaved maple, silver, 69 

Leaved trees, broad, 31 

Leaved trees, Ust of most important 

broad, 37 
Leaved trees, wood of broad, 31 
Leverwood, 65 
Life, tree of, 17 
Lime tree, 39 
Lin, 39 
Linden, 39 

Linden, American, 39 
Linden, downy, 39 
Liquidamber, 54 
Liquids, staves and heads of barrels 

containing alcoholic, 112 
List of important coniferous trees, 17 
List of most important broad-leaved 

trees, 37 
Live oak, 75, 76 
Loading, kiln cars and method of, 

Loblolly pine, 25 



Local distribution of water in wood, 

Locust, 66 
Locust, black, 66 
Locust, brown, 66 
Locust, clammy, 66 
Locust, honey, 66 
Locust, sweet, 66 
Locust, yellow, 66 
Lodgepole pine, 27 
Lombardy poplar, 79 
Long-leaf pine, 24 
Long-leaf willow, 84 
Long-straw pine, 24 
Losses due to improper kiln-drying, 

Lost in kiln-drying 100 lb. green 

Moist-air or pipe kiln, the, 188 
Moisture content, keep records of 

the, 249 
Moisture, demands upon soil and, 

Moisture on wood, effects of, 117 
Moose elm, 51 
Moose-wood, 70 
Mossy-cup oak, 72 
Most important broad-leaved trees, 

list of, 37 
Mountain holly, 65 
Mountain maple, 69 
Mulberry, 70 
Mulberry, red, 70 
Myrtle, 65, 70 

wood in the kiln, pounds of water, 

Nettle Tree, 62 


Noble fir, 21 
Norway pine, 25 

Magnolia, 67 

Nut, coffee, 49 

Magnolia, small, 67 

Nut hickory, black, 64 

Magnolia, swamp, 67 

Nut hickory, bull, 64 

Mahogany, birch, 41 

Nut, Illinois, 64 

Mahogany, white, 45 

Nyssa, 60 

Manner of evaporation of water, 


Maple, 67 

Oak, 70 

Maple, ash-leaved, 69 

Oak, American, 71 

Maple, broad-leaved, 69 

Oak, barren, 75 

Maple, hard, 68 

Oak, basket, 74 

Maple, mountain, 69 

Oak, bear, 74 

Maple, Oregon, 69 

Oak, black, 74 

Maple, red, 69 

Oak, bur, 72 

Maple, rock, 68 

Oak, chestnut, 73 

Maple, silver, 69 

Oak, chinquapin, 73, 74 

Maple, silver-leaved, 69 

Oak, cow, 74 

Maple, soft, 69 

Oak, duck, 73 

Maple, striped, 70 

Oak, dwarf chinquapin, 74 

Maple, sugar, 68 

Oak, iron, 74 

Maple, swamp, 69 

Oak, jack, 75 

Maple, water, 69 

Oak, laurel, 75 

Maple, white, 69 

Oak, hve, 75, 76 

Maul oak, 75, 76 

Oak, maul, 75, 76 

Meadow pine, 26 

Oak, mossy-cup, 72 

Method, choice of drying, 195 

Oak, over-cup, 72, 73 

Method of loading kiln cars, 206 

Oak, peach, 72 

Method of piling gum, 180 

Oak, pin, 73 

Methods, impregnation, 151 

Oak, possmn, 73 

Methods of drying, 154 

Oak, post, 74 

Mildew, elimination of stain and, 136 

Oak, punk, 73 

Minute structure, 34 

Oak, red, 74, 75 

Mockernut hickory, 64 

Oak, rock, 73 

Moist-air dry kiln, operation of. 


Oak, rock chestnut, 73 



Oak, scarlet, 75 

Oak, scrub, 74 

Oak, scrub chestnut, 74 

Oak, shingle, 75 

Oak, Spanish, 75 

Oak, swamp post, 73 

Oak, swamp Spanish, 73 

Oak, swamp white, 72, 73 

Oak, water, 73 

Oak, western white, 71 

Oak, white, 71, 72 

Oak, willow, 72 

Oak, yellow, 73, 74 

Oak, Valparaiso, 76 

Objects of kiln-drying, 168 

Odor and color of wood, 89 

Odor, weight, and figure in wood, 
grain, color, 86 

Ohio buckeye, 45 

Old field birch, 42 

Old field pine, 25, 26 

Operation of the blower kiln, 186 

Operation of the moist-air kiln, 192 

Orange, osage, 76 

Oregon ash, 38 

Oregon cedar, 18 

Oregon maple, 69 

Oregon pine, 29 

Orford cedar. Port, 18 

Osage orange, 76 

Out-of-door seasoning, 154 

Over-cup oak, 72, 73 

Papaw, 76 
Paper birch, 43 
Peach oak, 72 
Pecan, 64 
Pecky cypress, 19 
Pencil cedar, 18 
Pepperidge, 60 
Perch willow, 84 
Persimmon, 77 
Peruche, 21 

Physical conditions governing the 
drying of wood, 156 

Physical properties that influence 
drying, 125 

Pignut hickory, 64 

Pihng gum, methods of, 180 

Pine, American red, 25 

Pine, bastard, 26 

Pine, black, 25, 27 

Pine, buU, 25 

Pine, California white, 25 
Pine, Canadian, 25 
Pine, Carolina, 26 
Pine, Cuban, 26 
Pine, Georgia, 24 
Pine, ginger, 18 
Pine, gray, 27 
Pine, hard, 26 
Pine, hazel, 54, 60 
Pine, jack, 27 
Pine, Jersey, 27 
Pine, loblolly, 25 
Pine, lodge-pole, 27 
Pine, long-leaf, 24 
Pine, long-straw, 24 
Pine, meadow, 26 
Pine, Norway, 25 
Pine, old field, 25, 26 
Pine, Oregon, 29 
Pine, pitch, 26 
Pine, Puget Sound, 29 
Pine, pumpkin, 23, 24 
Pine, red, 29 
Pine, rosemary, 25 
Pine, sap, 25 
Pine, scrub, 27 
Pines, hard, 24 

Pine, short-leaf, 26 

Pine, short-straw, 25 

Pine, slash, 25, 26 

Pine, soft, 23, 24 

Pine, southern, 24 

Pine, southern hard, 24 

Pine, spruce, 26 

Pine, sugar, 24 

Pine, swamp, 26 

Pine, torch, 26 

Pine, Weymouth, 23 

Pine, western, 25 

Pine, western white, 25 

Pine, western yellow, 25 

Pine, white, 23, 24 

Pine, yellow, 24, 25, 26 

Pin oak, 73 

Pipe or moist-air kiln, 188 

Pitch pine, 26 

Pith and bark, 8 

Plane tree, 80 

Pocket dry kiln, the, 200 

Point in wood, the fibre saturation, 

Pole pine, lodge, 27 
Poplar, 67, 77, 79, 81 



Poplar, bay, 60 

Poplar, blue, 81 

Poplar, Carolina, 77 

Poplar, downy, 78 

Poplar, hickorj', 81 

Poplar, Lombardy, 79, 

Poplar, swamp, 60 

Poplar, white, 79 81 

Poplar, yellow, 81 

Port Orford cedar, 18 

Possum oak, 73 

Post borers, powder, 105 

Post oak, 74 

Post oak, swamp, 73 

Pounds of water lost in drying 100 
lb. green wood in the kiln, 179 

Powder post borers, 105 

Preliminary steaming of gum, 182 

Preliminary treatments, 151 

Pressure and vacumn, drying under, 

Pressure, drying at atmospheric, 146 

Prevent injury from insects, how to, 

Prevention of checking and split- 
ting, 129 

Principles of kiln-drying, under- 
lying, 166 

Problems in kiln-drying, unsolved, 

Products, crude, 106 

Products in the rough, seasoned, 112 

Products in the rough, unseasoned, 

Progressive dry kiln, the, 196 

Properties, characteristics and, 1 

Properties of wood, 4 

Properties of wood that affect dry- 
ing, 141 

Properties that influence drying, 
physical, 125 

Puget Sound pine, 29 

Pumpkin pine, 23, 24 

Punk oak, 73 

Pussy willow, 84 

Quaking Aspen, 79 

Range op Red Gtjm, 55 
Range of tupelo gum, 61 
Rapidity of evaporation, 124 
Recording hygrometer, the, 242 
Recording steam gauge, the, 246 

Recording thermometer, the, 245 
Records of the moisture content, 

keep, 249 
Red ash, 38 
Red beech, 40 
Red birch, 43 
Red cedar, 18, 19 
Red cedar of the West, 17 
Red cherry, 47 
Red cherry, wild, 47 
Red cypress, 19 
Red elm, 51 
Red fir, 21, 29 
Red gum, 54, 79 
Red gum, demands upon soil and 

moisture of, 56 
Red gum, form of the, 55 
Red gum, kiln-drying of green, 183 
Red gum, range of, 55 
Red gum, reproduction of, 57 
Red gum, second-growth, 59 
Red gum, tolerance of, 56 
Red juniper, 18 
Red maple, 69 
Red mulberry, 70 
Red oak, 74, 75 
Red pine, 29 
Red pine, American, 25 
Red spruce, 28 
Redwood, 19, 27 
Redwood, California, 19 
Redwood, Coast, 19 
Registering hygrometer, the, 244 
Registering thermometer, the, 246 
Rendering drying difficult, changes, 

Reproduction of red gum, 57 
Requirements in a satisfactory dry 

kiln, 160 
Ring, the annual or yearly, 10 
River birch, 43 
Rock chestnut oak, 73 
Rock elm, 50 
Rock maple, 68 
Rock oak, 73 
Rosemary pine, 25 
Rough, seasoned products in the, 

Rough, unseasoned products in the, 

Round-headed borers, 101 
Round timber with bark on, 106 
Rum cherry, 47 



Samples for Scalometer Test, 248 

Sand bar willow, 84 

Sap and heartwood, 8 

Sap, composition of, 116 

Saplings, 108 

Sap pine, 25 

Sassafras, 80 

Satin walnut, 54 

Satisfactory dry Idln, requirements 

in a, 160 
Saturation point in wood, fibre, 118 
Sawmills, scalometer in, 249 
Savin juniper, 18 
Scalometer in factories, 249 
Scalometer in sawmills, 249 
Scalometer, test samples for, 248 
Scalometer, the troemroid, 247 
Scalometer, weighing with, 248 
Scalybark hickory, 84 
Scarlet oak, 75 
Scrub chestnut oak, 74 
Scrub oak, 74 
Scrub pine, 27 
Seasonal distribution of water in 

wood, 115 
Seasoned and unseasoned wood, dif- 
ference between, 121 

Seasoned, how wood is, 145 

Seasoned products in the rough, 112 

Seasoning, advantages in, 128 

Seasoning is, what, 119 

Seasoning, out-of-door, 154 

Second-growth red gum, 59 

Sequoia, 19 

Service kiln, theory and description 
of forest, 161 

Shagbark hickory, 64 

Shellbark hickory, 64 

Shingle, heading and stave bolts, 109 

Shingle oak, 75 

Shining willow, 84 

Short-leaf pine, 26 

Short-straw pine, 25 

Shrinkage of wood, 130 

Shucks, honey, 66 

Sitka spruce, 28 

Silver birch, 42 

Silver-leaved maple, 69 

Silver maple, 69 

Slash pine, 25, 26 

Slippery elm, 51 

Small-leaved basswood, 39 

Small magnolia, 67 

Soft maple, 69 
Soft pine, 23, 24 

Soil and moisture, demands upon, 56 
Sorrel-tree, 80 
Sound pine, Puget, 29 
Sour gum, 62, 80 
Sourwood, 80 
Southern hard pine, 24 
Southern pine, 24 
Spanish oak, 75 
Spanish oak, swamp, 73 
Specialties, dry-kiln, 206 
Species, different kiln-drying accord- 
ing to, 170 
Species, temperature depends upon 

condition and, 171 
Species, weight of kiln-dried wood 

of different, 95 
Spindle tree, 82 
Splitting, prevention of checking and, 

Spring and summerwood, 12 
Spruce, 27 
Spruce, bastard, 29 
Spruce, black, 27 
Spruce, Douglas, 29 
Spruce, hemlock, 21 
Spruce pine, 26 
Spruce, red, 28 
Spruce, Sitka, 28 
Spruce, tide-land, 28 
Spruce, white, 28 

Stain and mildew, elimination of, 136 
Stave, heading and shingle bolts, 109 
Staves and heads of barrels con- 
taining alcoholic hquids, 112 
Steam, drying by superheated, 150 
Steam gauge, the recording, 246 
Steaming of gum, preliminary, 182 
Steaming of gum, final, 182 
Stock and wooden truss hoops, dry 

cooperage, 112 
Straw pine, long, 24 
Straw pine, short, 25 
Striped maple, 70 
Structure, anatomical, 14 
Structure, minute, 34 
Structure of wood, 4 
Stump tree, 49 
Success in kihi-drying, conditions of, 

Sugar berry, 62 
Sugar maple, 68 



Sugar pine, 24 

Summerwood, spring and, 12 

Superheated steam, drying by, 150 

Swamp Cottonwood, 78 

Swamp hickory, 64 

Swamp magnolia, 67 

Swamp maple, 69 

Swamp pine, 26 

Swamp poplar, 60 

Swamp post oak, 73 

Swamp Spanish oak, 73 

Swamp white oak, 72, 73 

Sweet bay, 67 

Sweet buckeye, 45 

Sweet birch, 41 

Sweet gum, 54, 80 

Sweet locust, 66 

Switchbud hickory, 64 

Sycamore, 80, 81 

Tacmahac, 79 

Tamarack, 22, 27, 29 

Temperature depends upon condi- 
tions and species, 171 

Test samples for scalometer, 248 

Theory and description of the forest 
service kiln, 161 

Theory of kiln-drying, 157 

Thermometer, the recording, 245 

Thermometer, the registering, 246 

Thorned acacia, three, 66 

Three-thorned acacia, 66 

Tide-land spruce, 28 

Tunber, 1 

Timber beetles, ambrosia or, 99 

Timber with bark on, round, 106 

Timber worms, 103 

Tolerance of red gum, 56 

Toothed aspen, large-, 79 

Torch pine, 26 

Tower dry kiln, the, 202 

Treatments, preliminary, 151 

Tree, abele, 79 

Tree, bee, 39 

Tree, button ball, 80 

Tree, coffee, 49 

Tree, cucumber, 49, 67 

Tree, fir, 20 

Tree, lime, 39 

Tree, nettle, 62 

Tree of life, 17 

Tree, plane, 80 

Trees, broad-leaved, 31 

Trees, classes of, 5 

Trees, coniferous, 8 

Trees, list of important coniferous, 17 

Trees, hst of most important broad- 
leaved, 37 

Tree, sorrel, 80 

Tree, spindle, 82 

Tree, stump, 49 

Trees, wood of broad-leaved, 31 

Trees, wood of the coniferous, 8 

Tree, tulip, 81 

Tree, umbrella, 67 

Troemroid Scalometer, the, 247 

Truss hoops, dry cooperage stock and, 

Tulip tree, 81 

Tulip wood, 67, 81 

Tupelo, 82 

Tupelo gum, 60 

Tupelo gum, range of, 61 

Tupelo gum, uses of, 61 

Types of dry kilns, different, 185 

Types of kiln doors, different, 231 

Types, kilns of different, 196 

Umbrella Tree, 67 

Underlying principles of kiln-dry- 
ing, 166 

Unseasoned products in the rough, 

Unseasoned wood, difference be- 
tween seasoned and, 121 

Unsolved problems in kiln-drying, 

Uses of the humidity diagram, 237 

Uses of tupelo gum, 61 

Vacuum, Drying under Pressure 

AND, 146 

Valparaiso oak, 76 
Virgilia, 85 

Wahoo, 51, 82 

Walnut, 45, 82 

Walnut, black, 44, 82 

Walnut, Circassian, 60 

Walnut, satin, 54 

Walnut, white, 45, 83 

Water beech, 44, 80 

Water by dry wood, absorption of, 

Water elm, 50 




Water in wood, 114 

Water in wood, distribution of, 114 

Water in wood, local distribution of, 

Water in wood, seasonal distribution 

of, 115 
Water lost in drying 100 lb. of 

green wood in the kiln, pounds of, 

Water, manner of evaporation of, 

Water maple, 69 
Water oak, 73 
Weeping willow, 84 
Weighing with scalometer, 248 
Weight, and figure in wood, grain, 

color, odor, 86 
Weight of kiln-dried wood of dif- 
ferent species, 95 
Weight of wood, 91 
Western larch, 22 
Western pine, 25 
Western white oak, 71 
Western white pine, 25 
Western yellow pine, 25 
West, red cedar of the, 17 
Weymouth pine, 23 
What seasoning is, 119 
White ash, 37 
White basswood, 39 
White beech, 40 
White birch, 42, 43 
White cedar, 17, 18 
White cypress, 19 
White elm, 50 
White fir, 20, 21 
White heart hickory, 64 
White mahogany, 45 
White maple, 69 
White oak, 71, 72 
White oak, swamp, 72, 73 
White oak, western, 71 
White pine, 23, 24 
White pine, California, 25 
White pine, western, 25 
White poplar, 79, 81 
White spruce, 28 
White walnut, 45, 83 
White willow, 83 
Whitewood, 39, 81, 83 
Wild apple, 49 
Wild cherry, 47 
Wild red cherry, 47 

Willow, 83 

Willow, almond-leaf, 84 

Willow, bebb, 84 

Willow, black, 83 

Willow, blue, 83 

Willow, crack, 84 

Willow, glaucous, 84 

Willow, long-leaf, 84 

Willow, oak, 72 

Willow, perch, 84 

Willow, pussy, 84 

Willow, sand bar, 84 

Willow, shining, 84 

Willow, weeping, 84 

Willow, white, 83 

Willow, yellow, 83 

Winged elm, 51 

Wintergreen birch, 41 

Wood, absorption of water by dry, 

Wood, beaver, 67 

Wood, canary, 81 

Wood, characteristics and proper- 
ties of, 1 

Wood, color and odor of, 89 

Wood, different grains of, 86 

Wood, difference between seasoned 
and unseasoned, 121 

Wood, difficulties of drying, 138 

Wood, distribution of water in, 

Wood, effects of moisture on, 117 

Wood, enemies of, 98 

Wood, expansion of, 135 

Wood, figure in, 96 

Wood, grain, color, odor, weight, 
and figure in, 86 

Wood, how seasoned, 145 

Wood in the kiln, pounds of water 
lost in drying 100 lb. of green, 

Wood, iron, 65 

Wood, kiln-drying of, 156 

Wood, lever, 65 

Wood, local distribution of water in, 

Wood, moose, 70 

Wood, of broad-leaves trees, 31 

Wood of different species, weight of 
kiln-dried, 95 

Wood of coniferous trees, 8 

Wood, physical conditions govern- 
ing the drying of, 156 



Wood, properties of, 4 

Wood, seasonal distribution of water 

in, 115 
Wood, shrinkage of, 130 
Woods, list of important coniferous, 

Wood, spring and summer, 12 
Wood, structure of, 4 
Wood that effect drying, properties 

of, 141 
Wood, the fibre saturation point in, 

Wood, tulip, 67, 81 
Wood, water in, 114 
Wood, weight of, 89 
Wood, white, 81, 83 
Wood, yellow, 85 

Wooden truss hoops, dry cooperage 

stock and, 112 
Worms, timber, 103 

Yearly Ring, the Annual of, 10 

Yellow birch, 42 

Yellow cedar, 18 

Yellow deal, 23 

Yellow fir, 29 

Yellow locust, 66 

Yellow oak, 73, 74 

Yellow pine, 24, 25, 26 

Yellow pine, western, 25 

YeUow poplar, 81 

Yellow willow, 83 

Yellow wood, 85 

Yew, 29, 30 

D.Van nostrand Company 

are prepared to supply, either from 

their complete stock or at 

short notice. 

Any Technical or 

Scientific Book 

In addition to publishing a very large 
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